To clear up the X-Men thing, there's no way a team up is happening. Basically, the deal is that Webb owed Fox another movie after 500 days of summer; in exchange for letting him do Spider-Man 2, FOX got to advertise in his movie.
As far as the actual film goes, I loved it, and it's right up there with the first two Raimi films as one of the best the character has seen. Foxx did a great job with Electro, and I actually wound up loving Dehaan as Osborn. There was a single shot, I think it was around the time of the board meeting, where his face, and, specifically, his eyes, made me go "damn, he really could be Chris Cooper's son." Overall, though, I really loved it. I don't think it was the greatest film of all time, but it was a solid comic book flick that fulfilled expectations. All of the performances were great, though, I particularly loved the bits between Peter and Aunt May; if there's one thing Webb seems to know, it's chemistry, because all of his characters really connect. That was an interesting side of that relationship, though, and I felt it was a particularly heartfelt aspect of the film, outside of the Garfield/Stone duo.
Garfield and Stone are absolutely fantastic together, though, and they have a very real spark. It's just a pleasure to watch them. Giamatti made me chuckle, I just loved his ridiculously over-the-top Russian bad guy; particularly when he was in a showdown with a seven year old. "Oooohhh, Spidad-Men ees heahd."
There was a cynical part of me that had him shooting Spidey as he talked to the little kid in my mind.
There was a lot of emotional weight to some parts, too. You really felt all that these people were going through and it made for an interesting dynamic between those darker dramatic moments and the super fun and energetic action scenes. I must say that one of the things I'm loving most about this franchise is its refusal to close doors, regarding villains. For almost the past twenty five years, it's become something of a trope to kill your bad guys in super hero movies, and it's nice to see a series where that isn't the case.