Minor deal alert here: Riddick is $6 on GOG right now. Very good game. If you check the Steam page my recommendation for it is up there.
We’ve talked almost not at all about this game, so if you haven’t played it, it’s probably the only example of a first person game that manages to juggle stealth, shooting, hand-to-hand combat, and role playing really well. Probably the best game about prison I’ve ever played. I don’t think there’s a PC demo available anywhere but I’m pretty sure there is a demo on PSN and Xbox Live. The game includes both an updated version of Escape From Butcher Bay and the extra mini chapter Assault on Dark Athena. I actually liked the latter as a sort of mini-story. Its only problem is that it seems to have a nice and acceptable ending… and then keeps going.