I have never liked
Blade Runner. Don't ask my why, because I don't know. It just left me cold.
Two of the
Star Wars films were in the top 4. That's cool. Not my favorites, but I like them.
Aliens was good, though not my favorite genre.
Lord Of The Rings isn't even science fiction. Loved them, but what are they doing there?
Matrix? Meh.
Serenity? Love it, glad to see it in the top ten, but would much rather it had been the full second season of Firefly. So while it's one of my all-time favorites I don't really consider it to be a movie, just cut-up segments from a TV show.
Alien? A slasher flick with monsters. Cool effects and I loved the cast, but also not really my idea of sci-fi.
Back To The Future. A lot of fun, but again not among my favorites, as in I don't own a copy or watch it once every year.
The Dark Knight? Maybe the best Batman movie, but again hardly science fiction.
But my own tastes are weird, so don't trust my opinion.