I really don't want to see a film full of Batman-villains. The Dark Knight was great because it really got to explore the character of the Joker because he didn't have to sacrifice his screen time. The later Batman films of the 80's had so many villains that none got the attention they deserved. Jack Nicholson was fun as the Joker because he had the time to really do something with the character. And remember the mess that Spider-man 3 had with its villains? Who could keep track of it all?

The Riddler would be awesome, especially if he was the only villain.