Just about all I play are early to late 1990's FPS games like Wolfenstein 3D, Doom, Doom2, Heretic, HeXen 1+2, Quake, Duke Nukem 3D, Shadow Warrior, etc. plus mods, wads, and TC's made for them. i have a lot of slightly newer games like Half Life, Unreal, Gunman Chronicles, Blood2, etc. but almost never play them. I like keyboard only games best.
This is my system:
Dell Dimension 4100 with an Intel Pentium III @ 1.0GHz
128MB SDRAM @ 133MHz
32MB DDR ATI Radeon 4X APG
40GB Ultra ATA Hard Drive
Win ME
8x/4x/32x CD-RW
Soundblaster 64V PCI

It works fine with almost every game I've tried.