Sersiously, what good is a live operating system that people will try out to see if they like linux without some awesome games?

My suggestions:
www.cubeengine.com The open source first person terrain generator (Like quake2, except better)

AND in the future when it's supported by some servers and perhaps a couple versions ahead:

www.sourceforge.net/projects/namc the open source MUD (MMORPG) client based on CUBE (above) to make (muds) truely fully immersive 3d experiences.