Joseph Gordon-Levitt is a lot like Robert Downey Jr. to me. I can watch both of them, and pretty quickly forget who they are in real life, and totally believe who they "are" in the moment of the movie.
We watched 50/50 last night, and it was NOT the laugh-fest we were promised. Talk about your poor marketing.
But it was great. Great enough that even though Ed and I wanted something funny, we couldn't stop watching it. Even to the point of pausing it while we went to the bathroom (that, FYI, is a sign that someone likes the movie - because you can still hear it in the bathroom - so if it's only OK=kay, you let it run).
He is a great actor.