SPOILER ALERT!: Why I [gasp] think it's a good movie...

This movie wasn't trying to be a masterpiece at all. It was just meant to be a fun popcorn flick, a VERY-tongue-in-cheek horror-comedy spoofing horror movies of its era. I like that it took itself HALF-seriously and HALF-jokingly -- often at the same time, for example, who the heck wouldn't be scared (at the age of 15, by the way) if you're taking a bath and a large green creature rises out of the water in front of you and roars, yet at the same time the concept is also ridiculous -- it works that way. Also, the heavy cheese factor is supposed to be there, hence the comedy/spoofing. I think people on this site are being MUCH too harsh about it; they weren't going for a CITIZEN KANE; and for what it is, it's definite fun (and not without suspenseful or intense moments, either)!
Some people are saying "it's so dated," and to that I say, 1981 was a VERY different time from now, did you expect them to have a crystal ball to see into the future and apply our fads, tastes, and styles to it? On a side note, I wonder what specific movies this was spoofing (apart from the obvious CREATURE FROM THE BLACK LAGOON), as I have seen horror movies from just a little later on that complement this quite nicely, like POLTERGEIST, GREMLINS, the original FRIGHT NIGHT, and TROLL. (I'm sure there are plenty, I just need to watch them.)
A final comment I have is that I've seen comments on here saying that SCARY MOVIE is "much better" -- I disagree (in spite of that movie also having an equal intentional cheese factor), because that movie's makers felt the need to make it as raunchy as possible, with everything displayed on screen, and I DO mean everything (but I'll stop right there should my post be otherwise deleted). I'm not easily offended, but I just don't find that to be particularly funny -- call me old-fashioned, I don't care. The fact that SATURDAY THE 14TH didn't have anything like that gave it a PG rating, and thus accessible to a wider audience.