I think it's a play on the whole "cowboys and indians" trope.
Personally, upon seeing this trailer, cast, and plot summary, I must say: I'm genuinely excited.
It's unique and original. It's two genres you've never seen meshed before, and based on the cast alone I have a good feeling that they might have meshed them well.
We as movie goers aren't willing to give strange new films a try it seems,and I hate it. Bet you all loved Inception, right? How many of you have seen Memento? Probably not as many as I'd like. Nolan wrote and directed Memento in roughly 05ish and it got very small numbers at the box offices, but oh ho, give him some star power with street cred like Batman and boom, whatever he stuffs out is pure gold. Not saying I didn't enjoy Inception, I just feel it was way hyped up on names and not so much on story (granted the story was awesome).