Thoughts on Main Characters

You have to be careful with extremes: when not done well, you end up with a full-fledged Mary Sue (or at least a Sympathetic Sue). I say proceed with caution unless you're 100% sure you can pull it off.

Personally, I think a Sue is just the product of a writer who doesn't have the skill to pull off the story/character, rather than an actual problem w/the character themself.

At first I was going to scream MARY SUE too (I mean just the phrase "cold-blooded teenage gang banger who specializes in assassinations" already makes my eyes glaze over with 'Look at me! Aren't I special and edgy?'-disease.) But on the other hand, how many books can I list that have a formula that goes:

boring average teenager + boring average circumstances?

I mean, yes, they exist, but it took me a while to remember some. I might say maybe the Sarah Dessen* books (though I think, obviously, an element you did not include in the equation is EXTRAORDINARY writing ability that makes even the most mundane topics interesting and relateable) but... Yeah, I definitely think it doesn't hurt to make characters and situations more unique and interesting than how they would be in real life. One of the aspects of reading is to be entertained, after-all.

* Sarah Dessen fans, please don't kill me!!!