In my opinion, the problem with the usage of MJ's character in Raimi's franchise was that she was the literally the basis for all of the things that drove Peter to do certain things (big things) throughout the films.
- He wanted to impress her with a new car, so he tries to make money at the Wrestling gig and we all know on how that went.
- Her life is threatened, hence the thing that leads into the climax fight with Goblin.
- He wants to have a normal life with her mainly, so he gives up being Spider-Man.
- He wants to have her and is pissed off that Harry forced them to break up, so he dons the black suit willingly despite being told not to, and we know what happens there.
At some point it got very boring, not to mention, as others have said, the way she was characterize made it difficult if not next to impossible to like her character.
Gwen's character from what I've been told from the film is a SEVERE IMPROVEMENT over Raimi's take on MJ, and I pray that whoever directs the film that introduces MJ will do wonders with that interpretation.