I just saw it this afternoon as well, and I too really liked it. I agree with Angel Of Light, in that this was definitely one of the better marvel movies. I thought it was a great first entry and definitely can't to see what Favreau has in mind for the sequel. The whole development of the suit was great, specifically the scene with the thrusters (hmm, that miniatre arc reactor technology he developed might make a good 4th year project). Haha and that bonus scene at the end of the credits, just awesome! Definitely stay after the credits if you're a Marvel fan.
Also, I was surprised by the number of great trailers this movie was carrying: Indy 4, The Dark Knight, and The Incredible Hulk (which actually looks pretty good). Iron Man is a great kick off to this summer's line up of movies.
Jam it back in, in the dark.