In no particular order these are games I liked or loved but all are worth a try.

Fallout 1 and 2, Fallout Tactics, Diablo Series, Realms of the Haunting, Blood 1 and 2, Duke Nukem, Baldurs Gate 1 and 2, Neverwinter Nights 1 and 2, Dungeon Siege 1 and 2, Time Commando, Everquest 1, Everquest 2, World of Warcraft, Warcraft Series, Command and Conquer Series, Starcraft Series, Advent Rising, Jedi Knight Academy, Jedi Knight 2, Knights of the Old Republic Series, Thief Series, The Witcher, Half-Life, Half-Life 2 (and it's mods), Doom 3, F.E.A.R., GUN, Oblivion, Albion (hardcore old school), Blood Rayne 2, Vampire the Masquerade, Jade Empire, Gothic Series, Fable, Star Wars: Battle Front 2, Beyond Good and Evil