The game launched with 4 days of early access for players who could cough up 20 dollars extra. This made it so many people who wanted to get the game instead had to watch it on streaming websites, where most of the popular players were trying to reach max level as quickly as possible, skipping big parts of the story and farming the same content over and over again, making the game seem boring as hell.
There is no real crafting of items. There are no chase items, so grinding makes no sense past level 100. There is an in game store where you can spend real-life money on cosmetic items, This is bad in a paid game, makes sense if the game is free-to-play, It also uses a currency you have to buy (Platinum), which makes it so you never get exactly what you need, either more or less, which makes many people feel like they have to get more and more... Predatory really.
The game looks good, it plays fairly well most of the time and the bosses for the most part are great. There are too few monster types, this makes the huge world they made seem smaller than it is. Some of the dungeons look fantastic, dark and atmospheric, but too many of them have boring objectives you have to complete, in some cases this makes you run back to get stuff you might have missed or could not carry with you the first time through.
Diablo 4 might be a nice experience for people new to the genre, but those who have been around for a while might get bored quickly.