The worst part is that they have used up the series' best villain in the second movie. None of the other Batman villains can come close to the Joker. Period.
I think unless you can get a crossover between Marvel and DC which pits Batman against The Hulk...or something along those lines, the third one is going to be majorly anticlimactic. With the Dark Knight they have set the bar so high that any movie following it, Batman or otherwise, is going to be very hard pressed to top it.
I hope they end the series right there. I'd rather see the franchise end right now than see it fall like Spidey did...
"Chickens are dope..." - Von Miller