ZQuake is a port of one of the most popular first person shooters, Quake, adapted specifically for Palm. That sentence alone should excite you.
But I have a few more. This adapted version supports different resolutions (normal, left-handed or rectangular), uses both the buttons and the pointer, supports infrared keyboards and even includes multiplayer mode via Bluetooth.
It's a little complicated to install, view 'Notes' below or the website for more info. But once you get it going, it is, of course, brilliant.