After spending the last few hours playing Diablo III: Reaper of Souls I can say that it is a very worthy upgrade to Diablo III. I started the new Crusader class and so far am loving it.
What are your spoiler free thoughts of Reaper of Souls? How did you start and where did you end off after your first day playing?
http://us.battle.net//d3/en/blog/13370216
Act V is awesome. There's so much going on. The level design makes it feel like you're more in a place than in a game level, and there's something new to do around every corner. You're greatly rewarded for exploring rather than just bolting for the next area, which is great for me because that's the way I've always played it anyway.
I just hit Act V myself and so far, I agree. There are lots of people to talk to and the amount of side instances and such is great. Not too far into it but I am having a ton of fun.
PS going through Act I-IV again was really fun too.