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.
As usual in most ports, the performance of the game depends on the technical resources of each device. And you need to have files from the original or demo versions of Quake 3D to be able to launch the game.
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.