Well, if anybody can pull a spiderman film off properly, it's good ol' Sam Raimi, he demonstrated that quite clearly since the first two films rocked and the third sucked more than a jet engine intake. It is only right to want to make ammends and apologize to movie goers and comic fans (like myself) by making a fucking good film.
As much as I like the Peter-Mary Jane-Gwen Stacy love triangle, they killed it for me because they didn't have the Goblin kill her.
I really love Venom and Carnage and that particular arc. The problem is, it's a very long story. How long you say?
:

raws huge breath...::
First you have include the creation of Spiderman with the Alien Costume, then have him get rid of it in order to create Venom be bonding him to a vengeful Eddie Brock. Then you have to have Spiderman (now back to his joy ol' red and blue costume) defeat Venom, separating the symbiote with Eddie. Then you get Eddie put in a mental hospital where he meets Cledus Cassidy, and then develop his character (a fucking psychotic serial murder). Meanwhile Eddie has to fall in love with a female psychologist/psychiatrist. Then you have to find a way for the sybiote to get back to Eddie, split and leave another for Cledus to get ahold of and create Carnage. They start running amok seprately and creating destruction and all that until foiled by Spiderman. They have to both be pissed on by Spiderman, and decide to team up to beat him. They get together and kick his ass very well, until you develop another plot point to get Eddie's love interest to confront him and try to stop him, only for him to ignore the stubborn "their's-still-good-in-you" type lady. Then it will take Carnage's really fucked-up mind to go too far and hurt the woman (maybe kill her) and then Venom will have to switch sides, and then develop a truce with Spiderman inorder to beat Carnage.
That's too long for a movie. That's an entire miniseries of comics right there. Movies can never capture the feel and depth of a comic anyways because motion picture ans print are entirely different media and present ideas much differently.
Plus, since they KILLED Venom (as well as cast Eddie Brock horribly wrong), he's gone. He's dead. He's out of the picture. They killed Harry Osbourne, so no Green Goblin 2/Hobgoblin. Kingpin was wasted on a crappily-don Daredevil, so no Sinister Six. ::sighs:: Kingpin was my favorite Spiderman villain and his Sinister Six.
I would like to see Lizard myself. He's already there (well Dr. Connors is): they mentioned him in the first movie and showed him in the second and third movies. In fact, in the below article Dylan Baker (actor who has portrayed Connors in the two films) said he would be excited to play the alter ego. http://uk.movies.ign.com/articles/757/757729p1.html
It is also rumored we may see Electro or Vulture. I would rather see Mysterio, Shocker, or perhaps Morbious (and a cameo from Wesley Snipes as Blade would be full of win).