If you're looking for something scarier, gorier and more intense than L4D, then I suggest you check out Killing Floor from Tripwire Interactive. The game is powered by the Unreal Engine. It's part of Steam's daily summer deals and is only $5 today, with the character skins are a mere 49 cents. Also, if you've been doing the daily achievements, you can get the Steampunk character pack for FREE!
Also, the Summer Sideshow event is already well under way:
Could really use more RH while playing this, playing with dumb randoms is beginning to be a pain in the ass.