I think its just because it takes Christmas, a normally joyful time, and adds murder in. I think it is a decent slasher film, but nothing great.
The slow grind to the end kills it for me. It's why I enjoy the remake more. It's a dumb fun slasher loaded with some really twisted and sickening deaths, and it doesn't pretend to be anything else.
Never seen any of those, though I have seen the remake of The Crazies. It was... okay. Better than most modern horrors as far as I'm concerned, still kinda shitty.
I guess I was tired or not paying close attention, when I watched it in theaters years ago, but I loved it the first time. Bought it on DVD a few years later, and I had to force myself to watch it two times since then.