Blizzard nailed Act V perfectly; it's long enough and the enviroment is dark enough for a Diablo game. I admit monsters are a pain in the ass, but only because they have abilities instead of walking at you like Act I zombies but it's fine.... what isn't ok is that if you get the Act V monster group in a GR, you can say goodbye to your victory and suck it up, which is stupid and we all know the reward for killing these bastards is too low.
Act 5 just sucks, sorry blizz