I saw it this weekend, and personally I'd have to recommend against watching it. Or rather, don't go out of your way to watch it. If you're looking for something to do some evening and want to check out a movie, it's not a BAD choice, however, it's not a very good choice either.
And considering how much I enjoyed Spider-Man 2, I have to admit I'm pretty disappointed. The fundamental problem with the movie is that there was just just TOO MUCH. Too many villains, too many problems, and nothing was fleshed out well enough that it was just a mish-mash of disconnected parts that didn't fit into a well defined cohesive story. Kind of like that sentence.
With the first two movies Peter Parker always dealt with three problems: 1. the main villain, 2. internal issues about being Spider-Man, and 3. Mary Jane. It was a formula that worked, especially with the second installment. Number 3 however, you have 3 main villains, there's no way in heck that each of them could be fully fleshed out. Then the internal issues were pretty lame and the whole MJ thing.
It was just a very shallow movie, and SM2 showed how much depth could be explored with the character, so it was just disappointing.
And there wasn't enough Venom! I mean he's one of the central villains in the comics, and he's barely in the movie! So lame.