A really fun and fast movie. Though the special effects are incredibly good (which surprised me, I've seen a lot of really poor CG stuff lately) what really makes the film work is the performances. Robert Downey Jr. is absolutely pitch-perfect as the hero and the supporting cast are all great, too.
The final battle could have been a bit longer after all the build-up but the very end of the film, specifically the final line, is fantastic and promises great things in the sequels.
I'd say this on par with the best of the superhero flicks, so...on the same level as X-Men 2 and Spider-man 2.