I wrote about this today but I think the success of this game will come down to one question, which is whether or note it is more like Diablo 2, or Diablo Immortal. It is already clear me to that it is NOT like Diablo 3, which I think is the best move. Just the addition (or should I say, reintroduction) of skill trees is a step in the absolute right direction. If they can get it closer to D2 -- where multiple builds per character are actually viable and fun to play, instead of D3's race to a single, best build per character -- they'll do alright.
Also I'm less concerned about obscene monetization because 1) they've already said monetization is cosmetic only and 2) they're smart enough to know that monetization ala Diablo Immortal is really aimed degenerate Chinese and Brazilian mobile gamblers who cannot help themselves. It doesn't fly nearly as well in the US market. D4 is supposed to be a marquee PC/Console title that will carry them into the second half of the 2020s. Overwatch 2 isn't looking to great, and it's not like the company has a deep stable of IPs to call upon. They have to get this right. Maybe that fear will get them thinking straight.