I've played Diablo since the day the first one came out. I really loved D2, hated D3 at first until they fixed a whole bunch of things (looking at you real money AH) and have just completed the main campaign in D4.
I do miss my superspeed WW barb from D3, I mean just absolutely blitzing a dungeon in under 20 seconds was always a ton of fun, but I've really come to enjoy the world building and story of D4 a lot. The mechanics are definitely pretty different in some aspects but I find that being forced to slow down and just actually enjoy the world is pretty great.
Looking forward to capstones, whispers, etc. and getting further into it. Are there issues with it? Sure, of course there are, but I think that things can only go up from here!
Really enjoying the game so far as well. The world building is great, music is awesome, and currently just been slowly going through the side quests, and some are surprisingly entertaining, and often have follow ups and contains references to d2 and d3.
I am playing a sorcerer and initially I had mana problem like everyone else, but I am slowly improving my gears and getting paragon points that mitigates that and improving the up time. It's funny to see so many other posts complaining about resource management in the mid game, when the game provides you so many tools that allow you to solve this puzzle and eventually just become a powerhouse.