I've seen a lot of reviews complaining about this film, all with the resounding message that the tone is inconsistent in this movie. I disagree. The only inconsistency I can see is the fact that this solid, straight-faced action movie has such a goofy, contemptible sounding title. If this movie went by any other name these arguments would probably never have cropped up. People went in expecting Snakes On Aplane or Kick Ass and got an entirely different movie.
Cowboys And Aliens
starts out as a fairly generic (if good looking) Spaghetti Western style plot. The man with no name enters a dusty border town and falls on the wrong side of a greedy cattle rancher. It plays as many of the typical, tired western tropes at once, but then the aliens turn up, steal all the gold, kidnap folk for experiments, and blow the shit out of the place.
This is a solid action movie. Daniel Craig and Harrison Ford are a delight to see on screen, in roles that make the most of their badass pedigrees. Even if there were no aliens and this was just the generic Western tale, this still would have been a good movie. But the juxtaposition of sufficiently creepy and vicious aliens keeps it fresh. The action is fun, and there is none of that jitter cam, jarring CGI, or fast cutting that plagues today's cinema.
In other words, it is everything you need in a solid action film. My only real complaint is that it isn't all that memorable in the long run. No action scene really stands out. They are competent and well executed, but they aren't quite inventive enough to stay with you. This movie is worth seeing in cinema or as a rental, but I wouldn't bother buying the DVD.