The real horror of the movie is actually the corporation behind it all, but with a creature dripping saliva all over the deck in anticipation of eating you, it's hard to keep that perspective. One of the all-time best science fiction horror movies, and there are things they got right on this one that they never duplicated (or decided to alter) in the sequels.
Scary, unpredictable, with a wonderful atmosphere and great performances. Cons: As typical with older scifi, especially when it was low budget at the time, it looks a little dated, but it's nothing major.