Have you tried Diablo? It's free to play on Battle.net unlike WoW. I recommend skipping the preceding games and going straight to the Diablo II expansion, Lord of Destruction. Seven characters with multitudes of ways to play each one. Throw in tons of monster types, pure evil, awesome dungeons, (including Hell!), and you get one addictive rpg.

P.S: You can play single player or mmorpg (multiplayer). Battle.net characters won't be playable on single or multiplayer, but you get exclusive items called runewords.