A perfect brain-smoothing game. Hold down buttons and watch demons explode and numbers go up. A little short (a friend and I maxed out co-op in two weeks), but really enjoyable!
One of the things that I think Diablo III does very cleverly (and that is now part of the genre, at least based on reading up on Path of Exile) is that they recognize the fun part of the game is the power creep and going from level 1 to being a whirlwind of carnage, which is why they've set up a seasonal system: every few months, all of your characters get wiped from online (moved strictly to offline so you don't lose anything), and you restart in the exact same game except with a couple season-specific tweaks and bonuses (extra treasure goblins, say, or more critical hits.) It keeps the game fresh because there's so little to do once you've hit the asymptotic part of the power curve but the journey is more fun than the destination.