+Sean Phelan on Google+ asked me about comparing 13th Age and D&D 5th edition. As a disclaimer, I've been playing in a 13th Age game for months, and while I've read through both the basic rules and the Player's Handbook for 5th Edition, I have only run about three session of 5th edition. So I have limited "live" experience.
That said, lets make with the comparisons!
Icons Versus No Icons
The first thing 13th Age introduces you to are the Icons, which are major NPCs that drive the setting. Most of them are designed to be pretty universal to fantasy settings, and your PCs have a relationship to them as a central theme to the game.
You have a certain number of dice based on your relationship with one or more of the Icons, and at various times in the game, the GM will be making rolls to see how that relationship effects the course of the adventure. This is pretty wide open, but it is stressed that this should be happening in the game. The PCs could get random help from their Icon, or from someone opposed to them (if they have a negative relationship), and at the beginning of the session characters should make these rolls to see what Icons might be subtly manipulating effects.
While D&D doesn't really have an analog to this, for anyone knowledgeable of the game system, its not entirely unlike how Obligation or Duty colors an Edge of the Empire or Age of Rebellion Star Wars RPG session.
Strictly optional in 13th Age, and mentioned, but not defined, although the Icons are given standard d20 alignments. Technically the default in D&D, although there are no longer any strict alignment requirements or mechanical connections in 5th Edition that I have found.
Similar terminology means completely different things in 13th Age and D&D 5e. In 13th Age, a background is something you invest a certain number of points in, and then when you want to make a skill check, you attempt to find a background that matches. For example, if your background was "second story man for the Thieves' Guild," you can probably justify using that background to make a stealth check.
This is a case where I'm actually more reminded of the background mechanic in Dungeon Crawl Classics than anything in D&D 5th, since D&D 5th uses backgrounds to help establish a series of personality traits that are used to guide roleplaying and measure the awarding of Inspiration.
Optional rules that give characters bonuses to do certain things centered around a given theme in 5th Edition D&D, in 13th Age, feats tend to be something similar, but are much more tightly focused on allowing a character to specialize in a given class feature or racial ability, and they aren't optional by default.
Armor and Weapons
While D&D 5th Edition has cleaned up and moved around the stats for various armor and weapons, individual armor and weapons still have meaningful stats. By that, I mean that plate mail has its own stats separate from chain mail, and a longsword is different from a warhammer. There is enough granularity in the game that those differences to matter.
13th Age really simplifies things by basically having heavy or light armor, penalties for characters if they shouldn't be wearing one or the other type of armor, and shields. Weapons do damage based on being light, one handed, or two handed, and this varies based on character class as well as size of the weapon, but not based on the weapon itself. So a two handed weapon for a wizard isn't going to do what a two handed weapon does for a barbarian, and there are examples listed by class for what they might be carrying that qualifies for each of these categories. This also means that rogues do more damage with a light weapon like a dagger than with a longsword.
Weapons are also where we start to see that 13th Age goes completely the opposite direction of 5th Edition when it comes to bounded accuracy and scaling damage. Weapons do their listed damage times the character's level. That means a fighter with a longsword at 1st level does 1d8 base weapon damage, and at 10th level does 10d8 damage. But we'll see this making more sense when we visit hit points.
Races in 13th Age have fewer more "flavor based" abilities rather than more numerous, more granular, rules that 5th Edition provides. Humans are reactionary, so they get to roll initiative twice and pick the best one, for example. As mentioned above, a lot of the racial abilities in 13th Age have feats that can improve them.
Like 5th Edition, races are arranged as "standard" races (Human, Wood/High/Dark Elf, Dwarf, Halfling, Gnome, Half-orc, Half-elf) and optional races (Aasimar, Tieflings, and Forgeborn). One of the Tiefling racial abilities also shows some of the difference between 13th Age's approach and 5th Edition's, in that the Tiefling's Curse of Chaos isn't overly defined and involves making stuff up on the fly.
This is going to be a large catch all for how the game is set up. 13th Age (like Dungeon Crawl Classics) organizes things into 10 levels. Its not that "someday we may do more levels," 10th level is meant to be uber-almost demi-god level. There is no bounded accuracy in 13th Age. In fact, there are three tiers to play (not unlike 4th Edition D&D), and hit points and damage ranges make larger jumps between the tiers than between the rest of the levels.
13th Age's reocoveries are similar to hit dice in 5th Edition, but they are worth more hit points, and there are more of them. While a GM could run a challenging campaign where players would need the edge provided by a cleric or a bard, it is also conceivable that players will have enough healing without any "in combat" healing from leader types.
Classes that have powers usually have them organized by At Will, Recharge, or Daily. There are classes that don't actually have powers, like the Barbarian or the Ranger, who just have class abilities that modify their normal attacks, or number of attacks.
Derived statistics for Magical Defense and Physical Defense, the stats that determine if non-weapon attacks harm you, are actually averaged from multiple ability scores, making it harder to assign a dump stat to a character, or perhaps easier to put your stats where they "should" go for the type of character you want to run.
Like 5th Edition, 13th Age asks a character to chose what "type" of character within a class they might be. Unlike 5th Edition, it's less about choosing a broad archetype that might have multiple mechanics tied to it, than it is actually choosing smaller class abilities that might make a character distinct. For example, you might chose an archetype in 5th edition that lets you be a weapon master, and then pick the bow as your weapon of choice, but in 13th Age you would just pick one of the archer class abilities to represent this. Each class has multiple class abilities, and to begin with you chose three (some classes have options that count as two of their three class abilities).
Just as the Tiefling has a racial ability that requires you to ad lib a bit and make up what it does on the fly, some classes, like the wizard, have abilities like this as well. Some wizards have very specific names and variants of the spells they cast, and if you can come up with a suitably grandiose variant title for a spell you cast, you can come up with some kind of extra kick that the spell has--its just something you make up, and the GM decides if they agree with the extra effect.
Combat rules between 5th Edition D&D and 13th Age are pretty similar, in that you roll initiative, roll a d20 and add a bonus to compare to a DC to see if you succeeded, do X amount of damage subtracted from hit points, etc. But the differences are once again in some of the narrative grey space that 13th Age likes to play with.
Movement in 13th Age is about being nearby, far away, or engaged to your opponents. No other ranges are really tracked, and the GM and players are told to do what seems logical within this paradigm.
The Escalation Die is a big deal when it comes to the difference between 5th Edition and 13th Age. In some ways, the Escalation Die is the what 13th Age did to solve the same issues that 5th Edition's bounded accuracy attempts to address. When numbers keep going up, and the defensive numbers keep up with the attack bonuses, you can have a lot of rounds of no one doing anything to anyone.
But every round after the first, the Escalation Die goes up, and this gets added to combat rolls for the PCs (and some iconic monsters, like dragons). This means that, as heroes, if the PCs can survive the first few rounds, they should be landing lots of blows towards the end of the fight. Rather than keeping things "close" by keeping the numbers close, as 5th Edition does, 13th Age starts out weighed in favor of the monsters and then swings hard towards the PCs.
Fleeing is another rule that 13th Age introduces that is meant to be a narrative based solution to what is going on in the game. If everybody wants to run from a monster that is too tough, they can. They get away just fine. Then the GM comes up with some kind of campaign setback. Maybe they escape the dragon, and it torches their hometown. Maybe they survive, but when they get back to camp, all of their horses and their treasure is gone.
Fighting in Spirit has mechanical effects, but requires some narrative justification. In 13th Age, if your character is missing from the fight or can't take actions anymore, you can fight in spirit. Effectively, this means you pick an ally and give them some kind of boost (if you have ever played Sentinels of the Multiverse, this might sound familiar). The challenge is that you have to come up with why that character gets a boost from someone that is not present. Did you give them a pep talk the night before? Do they have one of your old lucky charms? Did you give them pointers on fighting foes like they are facing now, and your words echo in their head?
Full Heal Ups are the equivalent of 5th Edition's Long Rest. A short rest can be taken, but all it really does is allow you to spend your recoveries before the next fight. The trick to 13th Age's Full Heal Ups is that you can't just rest 8 hours and get the benefit of them. You have to have completed at least four encounters before your extended rest to recover you powers and recoveries. This is to encourage a character to keep adventuring for a substantial period of time and not just blow everything in one fight and then rest. In some ways, its something 5th Edition addresses with getting back minor abilities with a short rest.
Holy crap is there hit point inflation. If you like zeroes, 13th Age is the game for you. The game accounts for the hit point inflation, but it is present. Not only does weapon damage scale to 1 die per level, but ability bonuses to hit points and damage start to jump between tiers, so your +3 on damage is eventually a +6 even if you never bumped that ability score, and eventually a +9.
Its hard to completely gauge this, because there is only a lose example of how this is suppose to work for 5th Edition so far, but the general thrust of it is not to throw something with a CR too high at the players, and then "eyeball" it, with an XP formula that can be used for more precise calculations. The overall idea is that you can throw "unfair" things at PCs if you telegraph that they may not want to deal with these baddies.
That said, a 5th Edition character trying to punch above their weight class is going to have a better shot at surviving and maybe even winning than a 13th Age character. Too many levels above their current level, and a 13th Age character will have almost no chance at hitting their opponent without the Escalation Die maxed out. Too far below, and there is no challenge to the PCs.
13th Age does encourage GMs to design "unfair" fights from time to time, although much of this is centered around how many enemies and what kind of nasty extra special abilities you give them, and not throwing something more than a few levels above their current level at them.
D&D 5e characters level up pretty quick at low levels, then take longer to get levels after the first few. 13th Age characters get levels when the GM determines that it makes sense for the campaign. This may be a set number of sessions, after an adventure is over, or every session.
Because 13th Age characters only have 10 levels,13th Age also has incremental advancements, which essentially allow you to pick one thing that you would get next level and use it now, if you didn't level up. So if the GM determines that you will get a level every four sessions, in session 2, 3, and 4 you will pick something that you get next level that you can use now (another spell, feat, hit points, etc.)
Another narrative flourish for 13th Age is that characters aren't suppose to level up until they come up with at least a rudimentary story for how they became more skilled, whether it's something mundane like training at a fencing academy for a month or absorbing the dreams of a dying dragon by breathing in their soul as it escapes in wisps of smoke.
Another game mechanic that has a similar name and different function between the two games. In 5th Edition D&D a ritual is a spell that you can take longer to cast without expending a spell slot to make it more of a utility. In 13th Age, a ritual is an open ended story element that you need to work out with your GM.
If you are a ritual caster, you come up with what you want your ritual to do. The GM tells you how much you need to spend to set it up, how hard your check will be to pull it off, and you expend a Daily or Recharge power to "power" the ritual. How hard and how expensive the ritual is will be based on how powerful and wide ranging the ritual is.
5th Edition has a few special rules for monsters, such as Legendary abilities and Lair abilities, which are meant to help set up some monsters as "solo" monsters and also to reinforce a certain mystique about them.
In 13th Age, something similar is done with monsters being either normal, large or double strength, or huge and triple strength. Double or triple strength monsters count as twice or three times as many monsters of their regular level.
Some monsters are escalators, which means they also use the escalation die, meaning that combat moves faster for both sides, potentially to the PCs' detriment.
In a manner not altogether unlike Lair or Legendary abilities, some monsters have abilities that trigger when they or an opponent have a certain condition, or that trigger when the escalation die hits a certain number. Some monsters also have abilities that trigger on an even or odd number on the die in addition to their normal abilities.
Monsters, in general, don't have the full range of stats that monsters in 5th Edition D&D have, having a more simplified stat block with the above listed special abilities listed afterwords, if present.
It seems to have become the trend in d20 level based fantasy to move away from buying "level appropriate" magic items and move back towards only utility perishables being available for sale. This is present in both 13th Age and 5th Edition D&D.
One big difference is that true magic items (those things you can't buy) have at least a rudimentary intelligence in 13th Age. PCs can only have as many magic items on them as they have levels, and if they go beyond this limit, the personalities of the magic items they carry begin to take over.
The magic item examples have quirks listed, but there isn't really a mechanical aspect to this. If you have four magic items at 3rd level, your magic items start making you do things, and if the player can't come up with good ideas for what this makes their characters do, the GM is encouraged to get suggestions from the other players.
My Humble Analysis
I'm not going to declare one system better or worse. Despite having similar mechanics and tropes, they do have a distinctive feel to them that sets them apart, and in my opinion, makes them better for different styles of games.
5th Edition D&D reminds me very much of the source material that inspires it. While your characters will eventually be able to kill ancient red dragons and even put the hurt on weaker demon lords, through most tiers of play D&D characters feel more like "action heroes" rather than full on mythic characters or super heroes. Your D&D characters may be the best of the best, but they still feel like the top tier of an existing class of people in the setting.
13th Age feels a bit more like playing mythological characters. With the emphasis on narrative resolution and the jumps in power between tiers, it really feels like characters that gain even a few levels in 13th Age are already likely some of the most powerful people in the setting, and by the time you are nearing 10th level, the Icons themselves are probably the only people that outclass you. This is less about playing Fafhrd, the Grey Mouser, or Conan and more about playing Perseus, Cu Chulainn, or Gilgamesh.