IMO I think they should have split the films into two parts as Alvin Sergent originally planned . He didn't go through with it due to the cliffhanger issue but there was just too much going on in 3 . It would mean restructering the story of course from the beginning but then again their were so many half baked and unfinished ideas that the script was in needed to be overhauled. They had Vulture, Sandman, Venom , New Goblin ,a "new love interest", The alien saga, the engagement, Spiderman being arrogant, MJ's struggles, Harry and his father issues, Eddie Brock all the running for Spiderman 3. They should have taken a few idea's and left the rest for 4 and 5 .
maybe Hobgoblin and Vulture , The forgiveness theme and Gwen's introduction in Spiderman 3
then for part 4 Have The Symbiote , Sandman, Venom , Peter's proposal, and MJ's troubles.
I dunno you could do alot of different combinations I guess ,.I just wish they had scaled back and be willing to leave certain idea's out .
@ one point Spiderman 2 was going to have Doc Ock, Lizard and Black Cat but they decided to scale back . I wished they'd done the same with 3.