As a diablo series lover(first time i beat it back on psx, it had coop, and was top quality), hell i even replayed og d1 back in summer 2017 and it still holds up, dunno even how many tousands of hours i spent in d2, i broke 2k hours in d2r, d3 i enjoyed for 300h, was right at launch of reaper of souls expack, never touched it after but i beat it with all classes and geared all 8 so they could comfortably beat max difficulty content back then.
Now about d4- i preordered it back in december, only spent 150h in it(for legendary hack and slash game its peanuts, ask any hardcore diablo or poe fan) and at lvl 77 i simply quit coz game was 0 fun.
D4 has great graphics, story and sidequests, it has extremly terrible itemisation and gameplay loop- so once u beat story and play a bit on higher difficulty u get 0 dopamine rush and simply quit coz of boredoom or keep playing and hate the game even more(thats what streamers did till they basically started throwing up with d4 and gave it really low scores, like 3/10;p).
TLDR no point playing d4 more than those dunno 30-50h when u beat story and/or finish all sidequests(again very fun, 0 complains here), but for lasting hack&slash game gameplay loop and itemisation is key, till it gets fixed in a year or two(maybe with new expack) 0 reason to play/come back to the game.
Big shame devs at the head, so responsible for most important thing fucked it up so hard when they already had all the info needed from d1, d2 and poe, d4 feels even worse than d3 at its core, just with darker graphics/setting :/