Movies that make you totally reevaluate your opinion of an actor.

To the OP:
Sean Penn has been one of the most respected actors in Hollywood for years. have you seen Carlito’s Way? Dead Man Walking?

Personally I think his performance in Casualties of War was one of the best pieces of acting I’ve ever seen. Roger Ebert has said several times that he thinks Penn is the best actor now working in films. {i]I Am Sam* was only about an average performance for him. You should really check out some of his other work.

I must admit I wasn’t too keen on George Clooney until I saw Out of Sight. Up until then all I could see was the doctor from ER. After seeing that I found myself wanting to see more of his movies.

Hmmm… none of these quite changed my mind, per se, but I was susprised by:

Sean Connery in The Untouchables. I see him as a cartoon character, you know? No matter what movie he’s in, he’s always Sean Connery. But he was actually good here.
I liked Clooney in O Brother in spite of myself. He did manage to shake off the pretty boy thing, somehow.
That’s a good call about John Goodman, greenphan. When used right (or used by the Coens, anyway), Goodman is fun.