Casting Robert Downey Jr. as Tony Stark in the first Iron Man movie was one of the best casting choices of any superhero movie that I can think of. Aside from Downey's remarkable talent as an actor, his real life struggles with alcohol and drugs added an extra bit of verisimilitude to a comic book character that deals with his own battle with the bottle. Comic books aren't often known among the casual audience for tackling weighty issues, so when one does offer a more three-dimensional glimpse into these larger-than-life characters, it's refreshing.
In Iron Man 2, Stark's alcoholism becomes an issue as his self-aggrandizing nature reaches new heights in the wake of revealing himself as Iron Man. What happens when an egotist is lauded for saving the world? Well, this movie tries to answer that question. The trouble on that front though, is that it doesn't do a very good job. The whole movie feels like an action movie weighed down at key moments when it tries to take itself more seriously than it should.
Overall, the movie is very enjoyable. Downey is pitch perfect as the jet-setting Tony Stark, and Sam Rockwell is just a treat to watch as Stark's corporate nemesis. Even Gweneth Paltrow is likable as Pepper, and I haven't enjoyed seeing her on screen in years. As for Mickey Rourke as Whiplash, well, he's Mickey Rourke so all he really has to do is stand there and be all Rourke-y. Then there is Don Cheadle as Rhodes, replacing ???. Cheadle counts as an upgrade in casting, as far as I'm concerned, but the Rhodes character is given very little development despite the amount of screen time. Aside from a couple of key scenes where Rhodes is at odds with Stark--one fight scene in particular comes off as cliched to the point of parody--Cheadle seems to be under-utilized.
Maybe it's just the fact that, as a sequel, this movie is tasked with being bigger, brighter, and louder than the original. There is only so much time for all these characters to be presented as their superhero selves as well as their mundane alter-egos. Where movies like Spider-Man 2 and The Dark Knight strike a balance and wind up becoming better films than the ones they sequel, Iron Man 2 struggles to make par.
If you liked the first Iron Man, you're bound to like this one. And as far as movies with "2" on the end of the title go, this one is a real treat.