Alien Trilogy was a good PS1 game.
It's pretty much your typical 1990's Doom Clone FPS game, but set in the Alien universe. Even if it can be a little generic, it is a solid game and I like that you have both Xenomorph enemies and human enemies who work for Weyland-Yutani like security guards, androids, and mercenaries.
Alien Resurrection for the PS1 is more like a Quake clone than a Doom clone, but it's a decent FPS for its time, and it's one of the few cases where the game was a lot better than the movie it was based on.