Not counting WoW, because reasons:
#1: Elder Scrolls III: Morrowind. Immersive, fantastic main/side stories, the content was incredible.
#2: Elder Scrolls V: Skyrim. Similar to Morrowind in gameplay, minus some immersion, story was great and plenty of side-story/optional shit to do.
#3: Fallout 3. Just in general loved the shit out of the game and expansions.
#4: Halo. Combined together, all four+anniversaries+Reach (not ODST because so bad). Played the stories multiple times each, and sunk quite a few hours into multiplayer.
#5: MOBAs. HoN/DotA/LoL. I'll throw them in the same boat because individually, nowhere near a lot of the RPGs I play in terms of gameplay hours.