A good "PS2-only" First-Person Shooter does exists! It's called Cold Winter!
The graphics are average at best, but they do the job. At least i don't recall having any problems with slowdowns... even with the craziest gun fights everything ran at a great frame-rate.
The sound is average as well. Nothing really stands out but at least the guns sound pretty good.
FPS Vets should have finished this game at around 10 hrs of playtime and without any huge difficulty. You have an unlimited health pack which makes the game really easy, but that's good if you are not looking for something frustrating and just wanna shoot people and enjoy a good story.
I would recommend this game as a rental to anyone who likes FPS with a good story.