I kind of agree with you here. I'd never taken him seriously as an actor purely because of his teen idol type image which I guess only came about because of Titanic. I remember watching him in Catch Me If You Can a few years back and thought he was pretty good and then watching The Departed and was very impressed, in fact I thought he was the best actor in it. Have now caught up with some of his other work and am still impressed (What's Eating Gilbert Grape - superb performance) and for his generation is probably one of the best around.
So, if he can rise to the challenge, then why not?