Diablo 3: Reaper of Souls
Through both additions and subtractions, Blizzard has done perfectly what few developers even manage to get right. Reaper of Souls is an absolutely mandatory part of the Diablo III experience. If you managed to wait through the less then stellar launch of the main game, you have absolutely zero reason to wait any longer. This is the game that should have come out two years ago, and while it's sad that we didn't have it then, it's great to enjoy right now.