I tend to be a bit leery when I see a comic book adapted on the big screen. It's completely hit or miss most of the time, but this movie is a definite hit. The adaptation is true to the original Iron Man story. It has been updated from the Jungles of VietNam to the mountains of Afghanistan, which worked very well. The actors are perfectly cast and do their parts very well. The chemistry between Paltrow and Downey Jr. is particularly entertaining to watch.
Overall it's well developed and the special effects are balanced with the story. Be sure to stay until the end of the credits: there's a great little surprise!
Go see this movie. I would even be so bold to say that this is better than the first Spiderman movie.