Dragon Age: Origins takes it for me. I ADORE fantasy and Dragon Age has it all: Impending invasion of evil creatures, a traitor who steals the throne which incites a rebellion and choices that feel like your actually influencing the world not just giving your character devil horns or an angel halo.
Gameplay wise the combat is challenging, brutal, bloody and tactically deep especially on the harder difficulties. Enemies aren't the most varied at times but there is quite a variety in how the encounters are placed as well as the composition of the mobs.
Bioware games all have great writing (if a bit too obviously cinematic at times) but Dragon Age doesn't suffer to bad and the characters all add either more depth and personality to the world and even annoying characters are well done, in their own way.
An RPG means many things to many people but to me I want to feel like a nerd when I talk about it with friends; that special ability to alienate the rest of the people in the group with talk of stat boosts, tier 8 volcanic aurumn weapons and Ulthemiel (Love that name)
But most importantly... Floating numbers and status afflictions as they are performed in combat. Watching that critical hit rise from a foe, the number 127 in larger than usual numbers and the significant drop in the elite boss Ogre Alpha health bar. Glorious.