Hard one! but I say Dragonage: origins!
why? well please let me tell you!
Good story, great gameplay.
the game was new and exiting at the same time as it was nostalogic to KOTOR and some fantasy games. the characters and factions all had an unique personallity to them. the voice actors actually emote!!!! (most of the time) and the feeling of freedom and personal choice was amazing! If you just could start killing randomly civilians it would be perfect!