Originally released way, way back a little after the release of the original Playstation; Acclaim's Alien Trilogy (you can tell this game is old considering the film series stopped being a trilogy when the fourth film Alien Resurrection was released a year later on) is a straight forward first person shooter in which you play as Ripley going through all the Xenomorph infested areas from the first three films.  By today's standard's the graphics, gameplay, and weapon options are all pretty dated, but in it's day Alien Trilogy was one of the better FPS games to hit the PS1.  All in all, if you still have your PS1 and dig older FPS games, you should give this one time gem a look.