Bah, you need dynamics, a grasp of ryhthm that is both tight and un machine like, plus an ability to play a melody.
Mostly i'd say you'd need an instinct for playing guitar. Not just a desire, but the instinct that you were actually born to play this instrument. No good guitarist i know is a guy who hides in his room n crys. They all think they are the shit, and with good reason mostly.
A big ego is a MUST, after all, the lead guitarist is the one people notice, on a par with the vocalist. I'm not trying to be judgemental, just sayin it how i think it is. If you havent got the balls to do it you probably should play something else. Thats how it goes for metal/punk/hard rock/ rock with any kind of squealy soloing in it.
(i'm a drummer, make of that what you will :P)