His choice to play less-than-good guys lately is one of the factors that keeps Johnny Depp on the top of his game. Every great actor has to play a villain occasionally, because they are more fun and more interesting, plus they often keep a falling actor afloat for a little longer (see John Travolta, Kevin Spacey). Before Depp went anti-hero in 2003 with Pirates of the Caribbean and Once Upon a Time in Mexico (not that either film was the first time), his star-power in Hollywood was starting to fade. The only thing is, one can't be creepy and kinda evil all the time, as he's been since then, except for in Finding Neverland. Plus, once going completely over to the dark side, it isn't always a given that it'll be easy to come back to playing the leading man part.
To play a vampiristic leader in the film I Am Legend, as he's rumored to do, will add another eccentric role to his resume, but will it make him even badder than we can tolerate? At least the latest version of Richard Matheson's novel should be somewhat comedic with Will "Aww Hell No" Smith in the lead, so it isn't like Depp will be playing too much for fright. Expect another quirky, campy character, who just happens to be the head of a blood-sucking population. Anyway, if there is one actor out there who audiences never accept as immoral as his characters, it is Depp. No matter how depraved he can be on screen, he continues to win the hearts of moviegoers, and audiences believe him to be a sweetheart in real life. I wonder what he'd have to do to make us believe he was really, really evil.