Omitting wow of course. I have spent thousands of hours playing wow off/on since 2007.
For me it would be
Elder Scrolls IV Oblivion, Mercenaries Playground of Destruction, Fable,Fable II, Knights of the Old Republic 1 and 2 mostly 1. Halo 2 Multiplayer. Counter Strike Xbox, Conker's Bad Fur Day live and reloaded xbox multiplayer. Dragon Age origins, Mass effect 2, Counter strike source, payday, payday 2, Dead Island. Warhammer 40k Dawn of war soulstorm and dark crusade. Lord of the rings battle for middle earth anthology.