20 Sci-Fi Movies EVERY Film Fan Should Have Seen

5. Aliens

We've already discussed that all too rare phenomenon of a sequel exceeding its predecessor, but it does seem that science fiction is the one genre that has successfully managed to buck the trend because it really was the gift that just kept on giving in the '80s and the '90s - and one of the best examples of that is, of course, 1986's Aliens.

That's right, watching Alien just won't be enough for any true fan because as excellent as it is, it isn't the franchise at its finest; no, in order to experience that, you have to come back for seconds and watch the James Cameron-directed sequel.

Building upon the world that its wonderfully slow-moving predecessor established, Aliens takes the franchise to new heights by doing the opposite. This time, Weaver's Ripley returns to lead an army into battle against the Xenomorphs on their turf - kicking off an adventure that is wildly action-packed, constantly jaw-dropping and unnervingly visceral.

It wouldn't be the only time that Cameron did the impossible by finding new highs for an already-perfect film series and that, along with his endless creativity, makes him arguably the best sci-fi director of them all. And again, Aliens is a thrilling example of why.