It's cowboys. It's aliens. What more did you expect?
007 (Daniel Craig) makes a bad ass cowboy. Harrison Ford is alright, but they don't utilize his full potential in the script.
The film is pretty good up till the middle point when you find out something about Olivia Wilde's character. Now I don't want to reveal what this is without spoiling the film, so you'll just have to use your imagination here. But once you find that out, it seems kind of cheesy and therefore the rest of the film falls flat with the same old, same old. After that it's just the usual big epic fighting scene between the cowboys and aliens and...yawn.
Overall, it's an entertaining summer blockbuster that effectively blends the two genres (sci-fi & western) into one, so it's certainly worth seeing. Just not the best movie that could've been made given the star power of the film's two main characters. Without them, this would've flopped around like a spaceship being driven by a drunk cowboy.