Venom was a step up from the comic version - but, as many have said it wasnt too hard to do.
Octopus was simply given The Lizards backstory, which made the character...stupid, IMHO.
Sandman was laughable. His "I'm not a bad guy" schtick was just hilarious considering his actions through the movie. You cant help but laugh at him and Pete enjoying a cry at the end together when 10 minutes before he was a giant sand monster smashing spidey's face in.
I always thought after Peter forgave him (LOL) and Sandy flies away, Pete turns to MJ and Harry's corpse just as a bank siren goes off. Far off in the distance "...I'm not a bad guy...". Peter sighs, fade to black