I have to say DiCaprio's really suffered from being the teenie girl idol in Titanic and Romeo And Juliet, but if you ignore those two and look at the rest of his career there's a bloody fine actor there.
From What's Eating Gilbert Grape all the way through to The Dearted, I struggle to think of a bad film he's been involved in (barring The Beach but it wasn't his fault he was miss-ast).
I'm no authority on Marvel comics, but I'm sure he'll be able to carry it off, he really is that good.