Paradoxically, I'm not too hyped over how obvious it is that Harry is going to be the villain in the next movie as the new Green Goblin. I mean, I love the emotional drama in the Spider-Man movies, I do, but I also like the action, and I don't want to have the third movie have the Goblin redux as the bad guy. While it's great for telling a story, I want to see a new villain on the screen.
Sadly, this probably won't happen. Sam Raimi said in some interview I read somewhere that he considered using multiple villains in this movie, and decided not to (rightly so), so that'll probably hold true with Spider-Man 3 also.