This is one of those films where everything that you need to know about it is in the title. The film is pretty much done as a straight-forward western, except for the fact that the villains just happen to be alien invaders.
I think it’s this western/sci-fi genre-bending that makes the film so fun to watch. It also helps that the film has a great cast that includes the likes of Daniel Craig, Harrison Ford, Olivia Wilde, and Sam Rockwell.
There were some slow bits around the middle and the look of the aliens (which are pretty much reptilian brutes) could have been slightly more imaginative. However, overall I have to say that I was quite entertained by this film.