Originally Posted by Picard Sisko
He was missing an arm, and that motivated him to work on cross-species genetics with Richard Parker. Of course, he really wanted to get his own arm back, and help everyone else with similar disabilities. After taking the serum, his plan to cure weaknesses was altered, even exaggerated, and this is where the film does fall flat, because they don't explain it enough. The serum pretty much turned him insane, giving him that "dual personality." But either way, we do know what he wants, and that is made clear... to turn everyone into Lizards. The Green Goblin just wanted Spider-Man on his side, and to kill "countless innocents again and again" until they were both dead.
No, that's what
he wants to do. It's not clear why
he wants this beyond the most rote, one dimensional, comic book movie screenwriting playbook cliches. It's Magneto's plan from the first X-Men but without the pathos.