http://frictionalgames.com/penumbra
Its a first person horror/thriller set in an underground complex of some sort in Greenland, and featues some pretty nifty ideas and oldskool puzzle gameplay.
I have to mention 1st the physics and how the player interacts with the world. Top open a door you have to click and hold the mouse and then drag the mouse in the direction you want to apply force to the door, thereby opening it, sounds simple but this mechanic is used for multiple things in the game and works great. Reminds me a little of that old game "Trespasser" with the virtual hands (that sucked) but thankgod the implementation here is solid and easy to control and really helps sell the immersion.
Which brings me nicely to the 2nd great thing about this game, the atmosphere. I dunno what it is about this game, but it really sucks me in, its just so creepy it freaks you out! The combo of doom3 style lighting and visuals, the player controled physics interaction, and the fact that you have NO WEAPONS to defend yourself just makes it terrifying.
Yes there is NO WEAPONS, this is not an fps, more of FPP (first perpon puzzler) like Portal etc, it does have some very oldskool puzzle elements such as combining items to create new items (this can be quite obscure at times) and using inventory items on the world.
Again this brings me nicely to the major drawback I found with this game, some of them item combos and world objects to use said items on can be very obscure and not clear at all, which does lead to frustration when you cannot find where to go or what to use items on. The game does have a handy notebook system to keep info on but its not enough, something I hope the developer fixes for the full product.
In closing, this game rocks, totally differrnt take on the horror/thriller genre and it works, it is created by an indie developer (just 3 guys iirc) and has cool motion blur :D
Please try this :)