Rather than tag this all, I'll just warn that
minor spoilers are below...
Saw it tonight. It was quite well done. As others said, it is not quite on the level of Iron Man but was still good. It was definitely better than Ang Lee's version; it moved along better and had better action scenes. I liked the way the Hulk was rendered in this one too. The detail was superb without hitting the uncanny valley (at least to me). Also, I liked how tall and relatively lean they made him. I found Lee's Hulk looked too bloated and plastic-y.
Geeky stuff that I enjoyed:
-The Hulk TV show piano piece was sweet.
-Ferrigno's cameo was good, as was Stan Lee's mandatory appearance.
-The purple pants thing was funny, as was the first appearance of the "You wouldn't like me when I'm angry."
-The reference to the World War II super-soldier program was great.
-Loved Downey's cameo.
-Foreshadowing the origin of the Leader.
For negatives, I found Norton's Bruce Banner a little too bland (he's supposed to be kind of bland I guess, but I thought he could have been given more personality.) While I liked the foreshadowing of the Leader, the actor was a little goofy to make an interesting villain (although I liked him as a character, he just wasn't intimidating at all). Also, while I enjoy Tim Roth as an actor, he does not have the appearance of a special forces commando; not only is he very short, he's got the physique of Mr. Burns.
Overall, though, I recommend it.