QUOTE (Fortune @ Nov 7 2008, 05:07 PM)

I don't really see the problem with letting a person play the character they want to play. I mean sure, you might find it less than ideal, or only two-dimensional, but if the player is having fun and getting what they want out of the game, why should you force them to add 'depth' they don't want to add, or become 'more creative' with their characterizations?
In my opinion, it is best to just let the player play the game the way they want to play it. Most players will evolve naturally themselves, especially when exposed to other players who put a lot of 'depth' into their own characters, or even better, a GM who isn't afraid to pour on the characterizations in the social scenes, and plays up the day-to-day life of the PCs. I don't feel that there is a need to 'teach' players to be better role-players, or force them into playing characterizations they don't really feel comfortable with, or aren't ready for themselves.
I agree with Fortune here. Players are going to play the kind of characters they want to play. Attempts to talk them out of it or into some new sort of character type is generally futile. I've got one guy in my group who always plays a maniac of some sort. Another one always plays a playboy of some sort. This is what they want to do, who am I to try and tell them to play something different?
So what should you do?
First analyze if you truly have a problem. Generally with loner emo types, the main problem that arises is that the players don't work together well and may be overly prone to backstab one another. If the players are more-or-less functional as a team, and there isn't to much intra-party mayhem that disrupts the game then there probably isn't a problem here. (Unless of course you want that kind of stuff, I don't, but to each there own).
If you are having these sorts of problems, talk with your players about it. Explain to them that for the game to work well they have to work together just a little bit. Consider having them make all there characters at once and having them share a common backstory of some sort. Give them some sort of common cause early on to unite them (having them betrayed by an employeer and out for revenge works well).
If your only problem is just that your unsatisfied with the character types, then you are probably experiencing some of these two problems:
The character types are just to bland. Give them incentives to develop a more creative backstory. Such as free karma point for ones that you really like. Get them to fill out the 20 questions (or some other equivelent). For my group I find starting each session off by asking a character an interesting question works well. I also like to do a mini-interview with the character, Pretend your Larry King and quiz the character about stuff, if possible get the player to respond IC as well.
You just don't like the character type: I completely understand what you mean, but well get over it. Yes the loner samurai who's parents, siblings, and pets are all dead may be a bit old hat, but if thats what the player wants to play, and its not disrupting your game, get over it. Your job as GM is to construct the setting and framework in which the players play, its there job to define and play the role of the actors, so let them do it. The game is (IMO) much more satisfing when players are playing characters they really want to play.
What you can do is provide some help and encouragement in game to help them grow. Have an NPC in the game befriend them. Kill off any remaining loved ones. Keep dumping drama on them until you get some positive results. You can also lead by example. Interesting NPCs can inspire characters to greater heights. Let the PCs know it's okay to steal blatantly for TV archtypes. (The emo loner often comes from a vain attempt at originality).
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But in the end you can only lead and encourage. Attempts to force the players to grow into character types you like better are bound to fail. Players are a lot like horses in this respect. You can lead them to water, but you can't make them drink.