Specifically, Talia being revealed as who she is, ruins Bane. During the whole movie, Bane had been built up to be this bad ass, who feels no pain, who escaped from the prison, etc etc. Then, right at the end, he is revealed to be Talia's bodyguard. And then Selina takes him out quicker than an anonymous cadet on a Star Trek episode vs the Borg.
And I think thats why I prefer TDK - the Joker. I liked Bane, although like some I couldnt hear him all of the time. He was pretty menacing. Its just that the ending made him far less menacing, because he went from a terrorist with a mission to a puppy dog bodyguard. The Joker, on the other hand, is as much a symbol as Batman is - he is pure chaos.
It did plod along in some places, too.