Honourable mention to Event Horizon, which is the only film to *really* have spooked the hell out of me. But that's really a horror film - the sci-fi aspect is just the scenery.
Same with pretty much all the Alien films except the last one, really - not what I'd call "science" fiction in any kind of purist way. I suppose genuine science fiction would be something that deals with the nature of science and its purposes and consequences - rather than just running away from space monsters.
Didn't like Event Horizon, thought it derivative - but the first two Alien films are great fun. After that - well....
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