I don't play Diablo IV (I just don't have the time), so I cannot judge if these scores are warranted. Seeing that it currently sits between Lego Drive 2K and Gollum, I'd go out on a limb here and say that this score seems a tiny bit harsh to me.
Games get review-bombed for the silliest reasons nowadays. Often times, a fundamentalist minority of gamers feels overly protective about "their" franchise, reacting to even the tiniest disturbance with maniacal anger. If a game has a high score from critics and a low score from users, to me that's actually a good sign that the game might even try something interesting (Last of Us II would be an example here). Of course, the critics score for Diablo IV was the post-release score, not including these new patches, so it might very well be that it really is worse now...