I really don't get why people were disappointed in this film, aside from readers of the graphic novel. It was a f*cking comic book move, what were you expecting? I know some people think TDK was a cinematic "masterpiece" (HA!), and maybe they held this movie to the same standards. This movie was clearly made to be an extremely comical, yet violent movie with splashes of melodrama. As long as you knew what you were in for before seeing it, it was hard to be disappointing (unless you were an idiot who didn't take it for what it obviously was meant to be).
BTW: I was afraid of hating Hit-girl before I saw it. The girl actually made the character very likeable, IMO.