http://devildaggers.com/
This came out yesterday. It's an arena survival FPS with some hardcore early 3D graphical styling. And it's fucking HARD.
I'm at the point where I can regularly survive for about 60 seconds. My best is 93. Some things to keep in mind:
Hitting "R" instantly restarts, letting you hop right back in when you fuck up/die.
Turn up the volume! Sound is extremely useful for telling you where things are around you and what those things are.
Steve is a noob: