I like the first Spider-Man. It had a well developed story with good characters. I thought Willem Dafoe was a great Green Goblin. I liked how all of the relationships were interconnected somehow, including the relationship between Peter and Norman and how Norman saw Peter as sort of surrogate son.
Spider-Man 2 is good. The action is tenser and stronger, but Raimi really piles on the angst-ridden drama. The conflict becomes a bit melodramatic and Doc Ock is a much weaker villain. He's very mustache-twirling without much depth or substance.
Spider-Man 3, on the other hand, is the worst of the series. It has too many storylines and too many characters without any of the subtle interweaving of the first film. The action sequences are also weak, since they are so sparse they lack the weight of the bank robbery sequence or the train sequence from Spider-Man 2 or the parade sequence from the first Spider-Man. Nothing stands out. It has some good moments (the first Sandman/Spidey confrontation, the funny tidbit with Bruce Campbell, and the moments before Harry gets amnesia) and some really bad moments (anything involving "emo" Peter, the Saturday Night Fever-strut, and that abhorrent third act). Overall, it's a big mess and a big missed opportunity.