Absolutely terrible. Which is especially saddening because I LOVED the last 3 Diablo games. I could go on about the problems, but the other reviews pretty much summed it up. For me, the most striking problem is the fact that the graphics, music, environment, gameplay mechanics and basically everything about the game have been changed so much that it's not even recognizable as a Diablo game anymore. Not that I can even hear the music most of the time.
It just feels like a generic Diablo clone with nothing to really set itself apart from other games. As an example, they made your character about twice as large as in any other Diablo clone I've ever seen. And this is in 4k. If I played at 720p, I could see the character taking up the entire screen. (Joking, I'm sure they downscale it).
In all honesty, I'm going to scrap this game and go back to playing 3. I don't know how you can screw up a game as good as Diablo, but they somehow managed to do it. Such a disappointment. This is why you don't buy games without watching gameplay footage first.