So cheesy, cliche, and sloppy at times. The script was just bad. The idea of aliens invading back in the old west days imo has potential to be something really unique.
Hate to say it but I also don't think Jon Favreau was really up to the task directing this kind of big budget film. Yes the Iron Mans were cool, but even then I don't think the action sequences were all that great, IM was buoyed more by comedy and RDJ (especially IM2 which had a particularly sloppy script). There was a whole bunch of bad staging. Characters standing around, then other characters just show up, with little craft.
I agree with everyone who says Harrison Ford was the best thing about the movie. Well done old man.