Spider-man 3 successfully continues the stories of Peter Parker, Mary-Jane Watson and Harry Osbourne from events of the previous film, whilst offering not one, but two new villains.
The problem is, this movie is so full of plot threads that each one only seems to get the bare minimum of screen time. The stories of Flint Marko/Sandman and Eddie Brock Jr./Venom could have used a lot more development, and I can only conclude that only one of the two should have been in this movie.
Peter's turn to the dark side was amusing, but under-utilised. The whole thing felt fast-tracked to get Venom on the screen. In the comics and the cartoon series, Peter's rivalry with Brock occurs over several issues/episodes and they gradually become enemies, which makes Brock's transformation and hatred that much more believable.
Similarly, the sympathetic note we're given to Sandman in the beginning makes it hard to believe that Venom can convince him to assist with Spider-man's destruction. This 'team-up' is also inconsistant with Venom's history as Spider-man's 'greatest enemy'. I just don't see it here.
I know this is sounding like a negative review, but aside from the 'bloated' feel, I enjoyed every minute. The characters, the humour and the action are all excellent, and the movie doesn't get dull or boring at any point, because I really loved all the character development and down-time scenes between the action.
The final two-on-two battle was wonderfully realised, making it's climax that little more emotional. This third film is clearly the end to a number of story threads, so any future sequels will have to explore new territory and characters.
On the grand scale, I'd say Spider-man 3 is better than 1, but not as good as 2. It does, however, make Spider-man the best super hero trilogy to date.