Starcraft goes down in history as my favorite game ever. If im going to categorize them...
Strategy: Starcraft, Homeworld series, and the Total War series
RPG: Neverwinter Nights, Baldur's Gate, and Morrowind
FPS: Ghost Recon, Half Life series and mods (most notably Team Fortress Classic and CS: Source)
Simulator: Silent Hunter III, Lock On: Modern Air Combat, and Falcon 4.0/ Allied Force