Found an amazing FPS (still in SVN development, but playable) built off the Cube 2 engine... it reminds me a LOT of Crysis 2 with some of the wall-running/jumping parkour. MAXIMUM HARDWARE enthusiasts, you should probably avert your eyes, but the non-demanding, beautiful open source graphics actually allow the game to run on a netbook I tested & my 3-year-old Mac.
Red Eclipse: http://www.redeclipse.net/