I watched Alien for the first time last night. Although I wouldn't say it scared me, it was certainly intense. I imagine that at the time the effects were more frightening than now. It was a good call to barely show the thing, but they still showed too much. Once it's clearly a man in a suit, it hurts the mood a lot. I definitely prefer the feel of this movie to Aliens, which I watched the night before. I'm glad I watched it first, too, because otherwise I'd have been so stressed out about the safety of Jones the cat that I wouldn't have been able to enjoy it. Jones is still alright in Aliens.
Aliens definitely shows the aliens too much. I know it's an action movie instead of horror, but they should still be somewhat frightening, and guys in suits just aren't. Also, minor complaint, but I don't think the redesigned, ribbed for pleasure aliens are nearly as disturbing as the original.
I don't have Alien 3, so I'll be skipping to Resurrection, which I have no confidence will be any good.