So far:
M&B Warband (grew very tired of M&B after 20 hours, but now I can run the good mods)
Payback
Tribes Ascend Starter Pack
Darkness II
Dead Island Complete
Killing Floor
Jagged Alliance 2 (which I had on GOG anyway)
Ghost Master
Complete Shooter Pack
Bob Came in Pieces
Zombie Driver
Caster
Hydrophobia: Prophecy
Nimbus
Back to the Future: The Game
Sol Survivor
Realistically, JA2 may be the only one of these I put more than 10 minutes into, but I hope to be surprised.