Borderlands 2
Unlike Torchlight II, Borderlands 2 is something that I can - and will - be revisiting on my own. That, to me, is the greatest victory in this sequel: that it's even fun to play solo. Maybe it's the robots.
That said, I've already conquered almost all of the main game's content, with the exception of the level-holy-fuck raid-boss. So it's a good thing that Gearbox is still pushing new DLC out.
Progress: Level 39, finished almost all quests (in Normal)