You can't make s**t shine. When you have the Harry Goblin story, a Peter/MJ/Gwen love triangle, Sandman's story, and then the symbiote storyline to tell, and then do Brock/Venom as well.
Waaaaaaay too much going on in SM-3. None of it worked. Only Harry's story came off in some way decent, and that's only because he's been getting developed since SM-1.
He was a petty criminal who just got his sand powers. He escapes from jail, chased by the Cops, falls into a pit and gets his sand powers. He just happened to be a petty criminal who was stealing so he could get money for his daughter.