Over all a solid movie: Ledger's performance was outstanding and the entire movie kept me on my feet. The action, story, and ideas were fantastic. However, I was disappointed with two things. First, (without giving anything away) the fate of the Joker seemed to not be enough for such an extreme character. Second, the villain that appears later in the movie (once again, trying not to give away anything) would have been great for a sequel, but wasn't developed enough for just an appearance in this movie.
Iron Man definitely ranks among the best superhero movies. The iron suit looks awesome, and Tony Stark is a very likeable and entertaining character. Without giving anything away, don't forget to stay after the credits, there is a bonus scene.