The show was pretty cute while it aired, but I wasn't particularly excited about this film. But they did go in a great direction with it stylistically, looks like they're going for the "epic" feel that I got from the series second season finale.
I also like that they went with "The Last Airbender" over a movie with "Avatar" in the title. I suppose it was partially a decision made to stop confusion with the other completely unrelated Avatar movie, but "The Last Airbender" just works well.
Generally I'd say that if I was going to see a martial arts movie, I'd watch an actual martial arts flick rather than the live action adaptation of a cartoon caricature of a martial arts flick. But this looks promising. I might see it.
Weird choice of director, I must say. Why Shyamalan? I'm not a fan of any of his movies. I suppose he's branching out? Where's the twist? =p