I liked it as well, but not as much as Cap 2 for pure entertainment. I sort of feel like Keg did, where I enjoyed the other aspects of the movie more in this one than some of the others, but the action wasn't quite up to some of the others.
The one thing that strikes me most about this movie is that it wasn't really what I expected at all...except it was? If that makes sense. I mean, obviously it is a sci-fi movie with humor and if I described it everyone would say duh, that's what we expected, but it wasn't really anything at all like I expected it to be. That's confusing, I know, but I was really surprised at how much it didn't go at all like I thought it would for most of the movie.
Definitely worth seeing, of course, and I'd give it a definite thumbs up. Just not as excited when I left the theater as I was after CA2 (and Avengers obviously). Not sure where I'd rank it really. I'd probably put Iron Man ahead of it too, since that one is really hard to beat for an origin movie. Better than both Thors (I wasn't a big fan of the second one like everyone else here).
EDIT: Oh yeah, Groot was awesome, but I think Rocket stole a LOT of the scenes, and was maybe the best character. Hard to not like Starlord of course, and he had his share of awesome, but Rocket really surprised me.