I have been playing since the original release of Diablo around 1997 and, like you, enjoyed D2 thoroughly. D3 was a rough start, but the introduction of seasons and rifts was pretty great. I liked the feeling of overwhelming power that D3 offered. D4 is a lot slower, a kind of calling back to the original and D2. I am enjoying the game overall, but there are some things that I would change given the opportunity. I find gearing to be less intuitive - hard stats may have been a better way to do it rather than percentages, but I'm no game developer. Although even at level 67 I am missing the feeling of power, in time I am sure it will come. At least one can cope. The sorcerer in D4 doesn't feel as good as it had in the past. To be fair I am running with 4 defensive spells which doesn't leave room for much else. I am struggling in WT4, but the drops in WT3 have been less than helpful in making my character stronger. The stats I need simply aren't dropping.
Overall though? D4 is excellent. Balancing and changes will occur that brings the game together and I have no doubt I will be playing this game for another decade.