The voiceover really doesn't add to the film. Some people like it, but I've read that Ford read the voiceover dialogue deliberately badly in the hopes that they'd drop it. Someone once described it as sounding like he read it with a gun to his head.

The other big difference is the happy ending in that first US theatrical cut. That's truely awful. I can completely understand him being very unhappy with it. The international cut is the same but for a couple of longer scenes involving violence.
The first director's cut wasn't by Scott, but it was based on his criticisms of the original cut.
The final cut is Scott's own version. I happen to like it the best.