Killing Floor is a lot slower paced than Left 4 Dead and has a smaller community, but the sheer gameplay and graphics of it more than makes up for its drawbacks.
You fight the "specimens" in waves, in between which you can buy weapons from the Trader, which travels around the map. There are a huge amout of weapons to buy and you can play differently depending on what perk you choose. It has low settings that still look decent and its max settings are amazing. Tripwire Interactive also update this game every month or two, adding new maps and content at no extra charge. This game is worth every cent and I've enjoyed it a lot.

This is the most amazing action RPG I've ever seen. The graphics create a highly realistic environment, the music is awesome, there are so many different ways you can play Skyrim to suit you, and they all have their own unique rewarding experience. The only thing that bothers me about this game at all is there are some bugs, "The Bethesda Touch" as I like to call it. But that'll be patched soon enough. 11/10. BUY IT!

An excellent game. It has been around since 2007 and has frequent updates thanks to the Team Fortress 2 community. A very tactical Class-based First Person Shooter, this game is well worth the $20.