I only played this for the first time recently.
The graphics are awful, the story is non-existent, the level layouts are archaic and the characters... well, there aren't any.
But GOD DAMN is it scary. Like, balls-to-the-wall scary. I love how it has both horror ("Oh Jesus when's the next Alien gonna show up!") and terror ("Oh Jesus the Aliens have showed up I'm gonna die!") in it. The confrontations are frantic and the pauses between them are nail-biting. Great stuff. Could've done with being a bit longer though.