When Downey was cast as Tony Stark, I thought that it was letter-perfect casting. In that film, and the subsequent Iron Man and Avengers films, he really came to own the role – the last line in the first movie, “I am Iron Man,” could have been said by Downey as much as it was said by Stark.
Marvel may make more movies featuring Iron Man after Downey steps down from the role, but they’d be foolish to try to recast the Tony Stark character. Also, I think it’s safe to say that the success of the first Iron Man film revived his career.
I enjoyed Downey’s Sherlock Holmes films, and it’s an interesting take on the character, but I truly think that Downey, himself, is better as Tony Stark.