The plot holes are egregious. The story is pretty cool, as a sci-fi fan.
This is more or less how I feel. The idea of humanity rebelling against an alien race after a millennium or so of being conquered is cool. Some action sequences are decent. Travolta is ridiculous.
Overall, it's bad, but I have seen much worse movies. I think it gets a lot of hate because it came out around the time that Travolta started to get a lot of publicity for being a crazy scientologist. This movie is a particularly easy target because it is based off of the book by L. Ron Hubbard.