Make no bones about it, Reaper of Souls is what Diablo 3 should have been to begin with. Blizzard has stripped out all the unnecessary mechanics related to their ultimately failed experiment of an auction house, while improving and expanding on what made the game actually fun to play. The difficulty system becoming more intuitive than a series of New Game Pluses and loot being regularly cool rather than rarely amazing are the most important of a huge slew of changes.
From the very start of the expansion's additional act, Reaper of Souls is bigger and better than what went before. Each map is both physically larger than earlier offerings and also crammed with events and dungeons. These are far more varied than before, too, no longer predictable winding corridors or samey combat arenas with barely-noticeable gimmicks. Each is a new challenge, using monster variety and clever environmental design changes to provide a refreshing, if still familiar, experience. This is echoed in the finales: the damp squib of encountering a boss less difficult than one of the randomly generated encounters is gone, replaced by individual, unique foes in their own right that require learning and skill to defeat.
It's a somehow even darker world, brought to life death by incredible music and superb use of light and colour. It's helped in part by not having to change tone based on transition between acts, but handles going from gothic city to swamp to angelic fortress with ease. The game itself evolves less obviously than before, however, keeping to a strict regimen of endless monster slaying. Adventure Mode has fixed the endgame by focusing that task and the new Crusader class manages to fill a tanky, more defensive niche - but if you didn't see value in it before, fundamentally it's the same game. Thankfully, that's just what I wanted.
Played for 12 hours.