Always nice seeing System Shock 2 getting some love. Ken Levine's brainchild, the same guy behind BioShock 1 & BioShock Infinite. SS2 is pretty damn difficult, too. One of the only games that actually made me think I wasn't supposed to progress. True survival horror. Also Postal 2? Hilarious.
Thumps up for Disruptor. Pc gamers went mad that wasn't released on Pc, I even knew two guys who while the had high end (and I mean really top system) pcs, they bought a playstation solely for Disruptor. And bear in mind, was that good that managed to impress hardcore pc FPS guys. Are you looking for FPS games just for the PS1 or for other systems as well? I mean, if you're into old school first person shooters, you ought to take at least a look upon Killing Time.
There used to be a very good site for first person shooters, but sadly it seems to be down now. You can still access it via the Web Archive, at: http://web.archive.org/web/20131206070859/http://3dsl.game-host.org/shooter/news/ (click on the year you want, or whatever, on the left-hand side of the screen, the complete list, called "A - Z Index" is quick loading too) but I don't know if the downloads will still work.