Really? I think The Avengers would be more popular than a dark Batman movie with a main villain that no one has ever heard of and another that they aren't promoting at all. Sure, the Avengers villain isn't popular at all but everyone loves The Hulk, Iron Man, Captain America and Thor, right? Plus, it looks FUN.
Most of the people that seem super hyped about the movie are big Marvel fans. I'm not saying that other people aren't going to see it, because that's not true at all, however TDK is the Wii of comic book movies, meaning it reached people outside of the typical audience for it.
The Hulk, Iron Man, Captain America, and Thor definitely don't have the wide appeal Batman has though.
The movie does look fun though, just like all the other big summer blockbuster movies (most notably Battleship later this month).
I'm expecting to see things blowing up/getting destroyed by Marvel characters for 2 1/2 hours and I'll be perfectly happy if what it turns out to be.