I use the following subjective ratings to classify my Science Fiction viewing consumption, including the SF films and SF TV I watch. In the perfect world, all my reading and viewing would fall into ratings 1, 2 and high 3s.
An SF "classic", that should be seen by everyone. Some classics are just excellent SF; others have contributed to the development of the genre and need to be experienced to get a better appreciation of the genre as a whole.
Good SF, well put together, with some definite depth to the plot, characters, or ideas. Definitely re-watchable.
A good enjoyable story, worth the time spent watching. Some may not be particularly deep -- or maybe not particularly SF-nal (just placing a plot on another planet, or in another time, doesn't make it SF). Some may be re-watchable.
It passed the time well enough, but I probably won't be watching it again.
I watched it, but wouldn't have if I'd known... (As a film, it was probably saved only because I had paid to see it, in the cinema: if I'd been watching on TV, I might have given up.)
I couldn't finish it because it was so bad, or boring, or whatever. Or maybe the style just didn't appeal to me. I probably said the Eight Deadly Words: "I Don't Care What Happens to These People" ... or Beings, or Artifacts, or whatever the plot is 'about'.
Dorothy J. Heydt, rec.arts.sf.written