So I had been unaware that this was a finite trilogy. Now that I know that, I find the new-villain-in-each-movie approach to be fairly disappointing.
It's not that you COULDN'T tell a continuous, long-form story capable of being told over 3 films with different villains in each one -- it's just that you've inevitably got to dedicate so much time to introducing those characters, giving them some semblance of a compelling character arc, etc. that your STORY is going to suffer for it.
Admittedly, the Nolan Batman trilogy has had some unforeseeable complications with continuity - Katie Holmes morphing into Maggie Gyellylgllylelglnahl and Heath Ledger biting it.
It just bums me out that now, when comic book movies are pretty close to a guaranteed thing - especially Batman movies - studios still don't have the balls to just tell a good character-driven story that doesn't devolve into crowbarring as many recognizable characters as possible into the films.