This came out on DVD recently so I finally got to see it.
First, Kaufman writes ingenious stories for film. There's nothing like them anywhere. Yes, there are familiar themes but structurally, they're some of the most unique movies anyone can watch.
That said, I think this movie would have been more successful had Kaufman not directed it. I think the auteur doesn't allow enough editing to go on script-wise and what's already an incredibly sad movie (which I have no problem with) is also plodding and boring at times. I nodded off often, waking up to loud noises and fantastic images.
The actors are great. Great fx, great make-up (as the cast ages some 50 years). And the concepts are the stuff of great sci-fi stories. But watching this movie was like traveling cross country on a train going really slow: long and no fun and once in a while you see something cool and you never want to do it again.