Now in the endgame and still having fun.
My main char is a Barb currently at lvl 92, not seriously pushing for 100 (so far) but got there just from grinding quite a bit for gear upgrades. Astronomically rare drops aside (i.e. Shako, Grandfather) he's well geared now in light of the current state of the game (things are still in flux and Blizzard makes changes frequently), and I feel I've now had the "full" D4 experience with that particular character.
Overall, the game has a number of issues currently, but those are mostly QoL things and certain mechanics being too impactful. Those should be relatively easy to address and I expect Blizzard will do so in the foreseeable future. In general, I'm very surprised how well made the game is. Graphics and generally the open world are stunning, the first playthrough was amazing, and characters have a good "feel" to them. The game strike a good balance in taking you by the hand first and but letting you go super crazy with grindy endgame stuff later on.
I'd say it's really a mix of D2, D3 and PoE, and a surprisingly good one at that. Many skills and general build archetypes are directly taken or clearly inspired from D2. Combat action and skill use/feel is similar to D3. And endgame progression and goals is a more casual "light version" of PoE (which remains the game for the most hardcore theorycrafting ARPG addicts, but the very complicated endgame optimization made it less accessible for more casual players).
To me, currently the least enjoyable aspect is the D4 community
even when engaging just passively just reading/watching content. PoE had a similar problem. Idiot content creaters being idiots, basically. It takes some time to sort through all the trash guides pushing poor builds, over-/underhyping classes or builds and complaining like teenagers about things that aren't really that much of a big deal,. You'll get a lot of those things on YouTube und various websites. One gets to the good information eventually, but it takes some effort and also a bit of own D4 gameplay experience to differentiate between the useful and the useless content.
Generally a super nice game. Not sure about the longevity of it, only time will tell ... but don't expect me around much for D2 around here in the near future.