I'm loving it as a base, and im sure it will develop well over the coming years.
Got my rogue to lvl78 and the done most of the aspects/side quests/statues etc.
My key areas that could be better are:
Hard CC in nightmare, as a rogue if i die its cause i was CC'd and nuked, some of it is just crazy, makes fishing for sigils a thing.
Items have way too many degrees of freedom, My dagger/sowrd are still way under leveled cause I cant get the right combo of damage boosting stats to match my lower level stat sticks.
Linked to the above makes enchanting items an absolute money sink, I spent millions in d3 to get 0.1% extra on an ideal build, in D$ im happy to get a "Not dead" stat for my build.
Paragon boards are great apart from the 10+ point pathing across the board to hit the node i want, feels like a road block in progression especially in later levels when its quite a grind to earn that XP.
I have 2 friends on XBOX playing and they crash a lot like 2-3 times a day this weekend. on nightmares that can mean a wipe, makes HC a no go until its fixed (that said i think HC is for masochists).
Looking forward to season 1, as someone who played all the Diablo games a lot and played D3 on/off from launch till last season I'm positive.