[PC][2000-2010] Old Time L4D Style FPS Shooter

Platform(s): Only played it on PC, not sure if it was on consoles.

Genre: FPS

Estimated year of release: 2000-2010ish.

Graphics/art style: It had a really grim and dark art style, everything was quite black, when enemies died they turned in to black dust or flies.

Notable characters: I remember there being multiple characters, one dual wielding pistols (not sure) and one with a katana.

Notable gameplay mechanics: It was really dark and quite spooky, it had some l4d vibes. You would go from one area to the other while taking on enemies.

Other details: Cats are better than dogs.