Talking to one of my gaming friends on Google+, I made an offhand comment about trying to figure out something that had to do with campaigns related to watching the Ghost Whisperer with my wife. While the show is definitely supernatural in theme, most of the time it isn't overly action oriented, so I figured it was more of a challenge than might be the case with a show like Buffy or Battlestar Galactica or something of that nature.
For anyone that doesn't know, the premise of The Ghost Whisperer is that there is a young woman with a gift for seeing ghosts and talking to them, and she figures out why they haven't moved on and helps them complete their unfinished business. However, while this is the main premise, after a while there are a few plot twists that veer into territory that gamers might recognize.
Long term murder plots, secret identities, lost cities, and sinkholes of souls trapped in despair started to make the meta-plot a little more action and horror oriented. But we already looked at meta-plots being layered over the initial premise and whether it enhances, reinforces, and augments the original premise, or if it causes some kind of overall thematic drift.
What clicked about the show upon watching it was that it actually convinced me that a type of game that I usually would say isn't a good idea might be possible in a campaign, under the right conditions. The lead character is (usually) the only one that can see the ghosts in the series. She has to do the heavy metaphysical lifting. In effect, she is the "chosen one," and the premise of the show doesn't work without her.
Normally, having a chosen one is a huge mistake in a campaign. One person with a destiny can be a problem. It diminishes the rest of the party, and if anyone else in the party can do what they do, it makes it difficult to understand one that particular PC is the chosen one, when multiple people in the party can do what they do. Finally, if the Chosen One gets offed or incapacitated, everything comes to a screaming halt.
So in a normal gaming group, I wouldn't recommend ever having a "chosen one" game. However, the more I watched the show, the more I thought it could be done, under the right conditions.
Conditions One: Players that are already comfortable with one another
It struck me that if I were running a game for my kids, or for my wife, or for some people that I've been friends with since I was in grade school, I think we could handle one of us being "the chosen one."
Gamers that are friends through gaming, and people that have known one another for a while might be able to handle this kind of trust and importance being put in one player, but it's more likely to show up with family or long term friends.
Also, with family and long term friends, if your "chosen one" becomes insufferable in their role, well, family and long term friends generally have incentive to actually work things out because gaming isn't their one primary link to friendship.
Condition Two: The play group shouldn't be too large
A group with five or six (or more) players is a bad fit for a "chosen one" campaign. Four or fewer really seems to be the key to this sort of play. For one thing, even if the other players are performing support actions, the importance of those support actions are going to be much more evident in a smaller group.
The smaller group is going to cycle through their turns faster, which means it should be easier to see how the actions of the whole group can be tied together.
There is also the added benefit of the the group cycling through their actions faster, and a smaller group ties into the next point rather handily.
Condition Three: The "chosen one" campaign shouldn't last too long
While a "chosen one" television series may last for years, a campaign with this concession should probably be limited to a few story arcs. Maybe nine to twelve at most. Enough to establish the concept, introduce a twist to the concept, ramp up the danger, then "save the world," for whatever that might mean in the given setting.
It also means that you can cycle through your three or four players rather quickly, giving someone else a chance to be the "chosen one" for a follow up campaign.
Condition Four: Make sure "chosen one" has some limits
On the show in question, the main character may be the only one that can see the ghosts, but if the ghost possesses someone, or if a murderer is on the lose, the other characters can clearly act against the possessed person, or the murderer. There is a limited but important reason for the "chosen one" to exist in the plot.
You don't want your "chosen one" to be Leeloo from the Fifth Element. You don't want your "chosen one" abilities to be "she's better than everyone else."
To put it in perspective, if you were running a 40K game with a "chosen one" theme, you might have only one character playing a psyker, getting premonitions driving the overall plot, and being needed to do whatever needs to be done for the final confrontation of the campaign. In a Star Wars game, you might have your Force Sensitive character serve the same purpose, or in a d20 kitchen sink fantasy game, you might only have one divine caster of any sort that has a direct line to their god.
Those characters are obviously important, and serve a role no one else can, but by nature of the design of the game, they aren't going to be the only ones that can be effective, just the characters that have the excuse for driving the plot forward.
A quick note on other "chosen one" characters that work
What I'm talking about in this post is a "chosen one" that has to exist for the campaign to work. If no one else can talk to ghosts, it's going to be really hard to find out what the ghost is upset about in order to put them to rest, and it's going to be even harder to have anyone else see the supernatural signs and portents that are pointing towards impending doom.
But there are other "chosen one" concepts that don't need to exist to drive the campaign. If you have a Slayer type character like Buffy in a campaign, there may be special abilities that only Slayers get, but if the Slayer is taken out, other people can fight vampires, especially after working with the Slayer.
If you only allow one Force sensitive character in a Star Wars game where you are playing a Rebel Alliance cell, that cell can still keep fighting the Empire even if the rare future Jedi buys the moisture farm early in the story. In fact, the death of the potential rebirth of the Jedi order could even galvanize the cell to redouble their efforts against the Empire.
You can make that same character into the kind of "chosen one" we talk about here, if that person is needed to receive signs from a higher power as the only means of the plot advancing, and if that person has to show up in order to resolve the final conflict of the campaign. But if they are just unique because you want the flavor of those characters to be rare and special, that's not the kind of "chosen one" we're talking about here.
So, I Can Do It, Why Do I Want To Do It?
The "chosen one" trope is something that shows up a lot in media. In some ways, pulling off a particular type of campaign for a GM is the roleplaying equivalent of scaling a mounting: you do it because it's there. There is a rewarding feeling to knowing you can pull off a convention from one type a media and translate it into the kind of storytelling that roleplaying can accomplish.
Another reason is to reinforce that the supernatural or what have you is rare and special. Having exactly one character in the campaign that can use their supernatural abilities to move the plot forward means that the group doesn't begin to subconsciously think that there are psychics waiting to take over that "role" around every corner in your world.