As a Windows user who has played all three games in the Penumbra series a long time ago (well... two years ago), I was kind of expecting more of a reaction to the actual gameplay from the Linux world.
Penumbra took a different approach to the traditional style of first person games and decided that giving you a fighting chance was way less fun than just making you wonder if you're alone in the dark or not. Penumbra: Overture allows some meager defensive tactics, such as swinging a hammer or saw in order to... fend off whatever might be interested in you. The second game, Penumbra: Black Plague, is the shining pinnacle of this development. No defense, no weapons, nothing that protects you from the mysteries in the dark. You can run, but you certainly can't hide very well (the panic system ensures this). The puzzles are challenging and require thought, but not in the "adventure-game-click-everywhere-until-you-don't-die-and-then-reload" style ala late 80s/early 90s Sierra games. Most of the puzzles are logical ones - there's a hole in the wall and you're hearing odd noises, and the lights are flickering. It's probably going to be a good idea if you can block whatever is in the hole - look around and find a crate or a box you can push to block it.
Unfortunately, Penumbra: Requiem took a step back in storyline and atmosphere and focused almost entirely on physics puzzles, sacrificing what Black Plague had as an excellent compromise for the sake of making something a bit different. I hope more game companies, Linux, Mac, or Windows, adopt newer styles of meeting a genre such as this game.