Cowboys & Aliens does not break new ground except that it combines two genres that I have never seen combined before: Western and Alien Invasion. The story is essentially a western from beginning to end, although in this case the bad guys are aliens from another world. You could have substituted any classic western villain for the aliens and the movie wouldn't have been much different. The movie is not the best western I have ever seen, but it is not bad.
The movie does gives us some interesting eye candy to look at with spaceships flying about and high tech gadgets. The trailer looks cooler than the movie because the trailer places greater emphasis on the alien invaders.
The aliens are fully realized. They appear like a cross between Predator and Alien. We don't get much sense of personality except that they are aggressive and like to experiment on humans. We are told that they came to Earth to mine gold which is "just as precious to them as it is to us." Somehow the thought of "greedy capitalist" came to mind, which is often a classic western villain. You would think that any high tech civilization wouldn't need to invade another world just to get gold. I guess that humans weren't the only ones who participated in the gold rush.
Daniel Craig's character has a lot of "The Man With No Name" in him except with less style. On the other hand, Harrison Ford's character is a bit of a pleasant surprise. He plays a rough hardened rancher with a bit of a mean streak that is a far cry from his usual hero character. In this movie he looks less like Harrison Ford and more like Geoffrey Lewis. He has a face that has been around the block a few times.
There are a few goofy moments like the aliens using lassos to capture humans and a man jumping from a horse to a flying craft. Native Americans use some sort of potion to restore a man's memory, and there is some symbolism of a hummingbird representing the spirit of the man's dead wife.
I have couple technical complaints: The scene of a cabin near the end appeared out of focus. I found my eyes trying to correct for it. Also, there is one scene that appears to have about 50 riders on horses, or at least that is what I expected from what was described in the movie, but when the scene switched angles it appeared only to be about half as many.
I have been excited about this movie coming out for months. Although it did not live up to my highest hopes, if you like western and/or science fiction then it is not a bad way to spend a couple of hours.