If you are expecting Spider-Man 3 to be the best so far of the franchise, I have to warn you that you will be disappointed. Of the three movies, it is the least of them all. That having been said, if you go in simply expecting a superhero movie with some good action scenes, some great special effects, and some humourous moments, then you might well get what you paid for.
To a large degree the problems that prevent Spider-Man 3 from being as good as either Spider-Man or Spider-Man 2 were simply bad choices made from the very beginning. One of these was the decision that Spider-Man 3 would feature three villains. Originally, Sam Raimi wanted to use Harry Osborn (as The New Goblin), Sandman, and The Lizard (who is Dr. Connors transformed into a bipdedal lizard, for those who haven't read the comic books). Avi Arad, then president of Marvel Comics claimed that he needed to use Venom because "The fans love Venom. He is the fan-favorite. All Spider-Man readers love Venom...(which only tells me that Arad was really out of touch with his fans)," so Venom was in and The Lizard was out. Either way, I think three villains is bit too much for any one superhero movie. Ultimately, one of the villains is going to be given far little screen time and is going to come off as more of a caricature than a character. This was a problem that plagued the later entries in the Nineties Batman franchise. While Spider-Man 3 does not suffer quite as much as the later Batman films, it does suffer. While The New Goblin and Sandman are well developed characters, Venom is little more than a cardboard cutout--a comic book monster for our hero to defeat.
Of course, this brings me to another bad choice, namely the use of Venom. If they had to use a third villain, The Lizard would have been a better choice. Contrary to Avi Arad, most Spider-Man fans I know actively hate Venom. Quite simply, he is a product of the Eighties fad in comic books towards "dark" characters. And Venom still displays the traits of such characters. He has no personality of which to speak. He has no complex motivations for his crimes. To sum it up, he is just a cardboard monster created for our hero to fight. While part of the reason Venom appears to be such a simple character in the movie is that it dedicates only a little screen time to him (preferring to devote it to Flint Marko, AKA The Sandman, Harry Osborn, and Peter and Mary Jane), that is only part of the reason. The other (and perhaps more important) part is that the comic books gave screen writers, Sam Raimi, Ivan Raimi, and Alvin Sargent, very little to work with. Even in the comic books, Venom is not much of a character. Even in the comic books he is a walking cliche.
Another bad choice to me was the inclusion of Gwen Stacy. No, I am wrong. Actually, the bad choice as utilising Mary Jane as Peter's love interest from the first movie onwards instead of Gwen Stacy. Let me make something perfectly clear, in the comic books at least, Gwen Stacy has always been Peter's one true love. The only reason that he ever wound up with Mary Jane was that Gwen was brutally murdered by the original Green Goblin (that's right, Norman Osborn) in a historic issue from which the first film took its climax (Amazing Spider-Man #121, June-July 1973, if you afford to buy it...). Including Gwen in this film, especially as mere eye candy and a paper rival for Mary Jane seems to me an insult to all of us fans who had hoped Gwen would be featured as his true love in the first movie. Let's face it, would the average person had been happy with the classic Christopher Reeves Superman if Lana Lang instead of Lois Lane had been his one true love in that film?
Of course, this brings me to another bad choice on the part of the screenwriters. Quite simply, that was to add unneeded complications to Peter's romance with Mary Jane. Indeed, at one point Spider-Man 3 simply descends into soap opera. Personally, I could feel the rest of the audience getting restless for the next action scene. And, quite frankly, I found Mary Jane to be a very unsympathetic character in the earlier part of the movie. Instead of being happy that Peter is finally being appreciated for saving lives and risking his own life as Spider-Man, she expresses frustration that he isn't paying enough attention to her because of her failing acting career (never mind, that he showed up to her debut performance in a Broadway musical, has always told her she has talent, and expressed plenty of sympathy for her when things started going bad for her where acting is concerned...). At one point Peter even apologises to her for being selfish; from where I sat, Mary Jane was the one who needed to apologise.... Maybe it was poor writing, but Mary Jane just came off as self-centred, clingy, and selfish in the first half of the movie to me.
Here I should state that, despite my rants above, I did not hate Spider-Man 3. Although it has its flaws and it isn't as good as the first two movies, it is worth seeing. In fact, I dare say that Thomas Haden Church's performance as Flint Marko is worth the price of admission. Flint Marko is ultimately a tragic figure, a man forced into a life of crime by the economic realities of his world. Worse yet, he finds himself transformed into The Sandman. Church, whose talent I've admired since the late, great Ned and Stacey, easily gives the best performance in the film. Also worth seeing is J. K. Simmons as J. Jonah Jamesson, who, as in the first two films, is easily the funniest character in the movie. And Stan Lee has his best cameo yet!
And while the film has no fight scenes that match the battles royale between Doc Ock and Spidey from the second film, it has some impressive fight scenes nonetheless. There is an early struggle between Peter and The New Goblin which is very good (I must say, I have to admire what Harry did with his father's technology). As impressive as the fight scenes with The New Goblin are, however, they pale compared to the fights between Spidey and The Sandman. Sam Raimi certainly makes the most of the character, utilising his power to change himself into mouldable sand to its full advantage. While the climax to the film does not match that of the second film, it is still impressive, with Spidey facing both The Sandman and Venom. Worse still, The Sandman apparently has more sand at his disposal...
Here I must point out that the special effects in Spider-Man 3 are perhaps the best of any of the films. The Sandman is realised as a realstic looking character--at no point when he changes into sand does it look like CGI. And the extraterrestrial goo that becomes Spidey's new suit (and later something else entirely...) is wonderfully made real. Indeed, here I must point out one of the film's charms is that Sam Raimi has not lost his touch when it comes to pop culture references. The sequence in which a meteor delivers the goo to Earth is a great homage to that classic bit of schlock, The Blob. And like the other movies, the film features yet another great cameo by Bruce Campbell (whom I would love to see appear as Kraven the Hunter in one of the movies to come). Yet another great sequence is when of Jameson's advisors tells him which papers in New York are doing better than the Bugle (even the Daily News!).
Over all, Spider-Man 3 is worth seeing. But I have to warn you that you should not expect a film as good as the first two. And I must also warn you that you will have to sit through some long sequences in which there is little to no action. Ultimately, however, I would say that the movie does have its rewards.