Back in the older days (I sound old now and I'm only 13 rofl) I liked to play DOS games. I played Duke Nukem 3D, Shadow Warrior, Blood, Jazz Jackrabbit 2 and Quake 2.
Old, but awesome games. The Quake engine was used to make games like Half Life, Counter Strike, Source games and even Call of Duty. (CoD was made off an engine that used the quake engine)