Well, I just got back from seeing it.
It was OK, if a little uneven pacing-wise. And for some reason I cannot explain it left me feeling... dissatisfied.
I have seen the first one five or six times now and still enjoy it. This one... I'm not going to see it again till I get the DVD. And even then, I get the feeling its going to be sitting on the shelf unwatched. Updates on further reflection
I think I will add disappointing to the above description.
Spader and RDJ were phoning in their performances. There wasn't really any flash from Stark at all, not like in previous movies. Tom Hiddleston was on fire in all his appearances as Loki, but most especially in the first movie. Spader was just.. there.
And really, if you've seen the trailers and the clips... well, you've seen the movie.