Diablo 4 is completely online. The art in the game is gorgeous, but the actual movement of your character is sloggy and tedious. If you don't have ultrafast internet you click and then wait forever for things to happen. In diablo 3 things would happen, and then occasionally here and there you'd have a problem maybe once a day. Now it feels constantly like dozens and dozens of times an hour. The extremely unresponsive online aspect ruins it for me.
There's a ton of running around to do miniquests, like fetching an item. Everything scales really hard and so your gear dies pretty bad. You feel like you're fighting the controls to get something to move in contrast to diablo 2, poe, or lost ark. In other games you click and things move.
Each season everything you grinded resets. In diablo 3 i could do everything in about 20-30 hours for a season ~120 tier dungeons. The dungeons in diablo 3 literally are just fetch things. It's horrible. There's 150 dungeons and not 1 is fun.
It's a really miserable seasonal grind. It doesn't feel fun at all. Season 3 is much worse than season 2. Season 2 had a simple powers system that was pretty easy to use and a fun little story about stopping a vampire. Season 3 has a really dumb vault thing where there's traps and an anti-climactic story. You click and your character doesn't move and you lose 3-4 levels in a trap. Most runs I don't get loot because of lag.
I just wish the D4 devs would make games that were responsive and fun.