I think people who played Diablo before are either going to like it or be put off, so there's no real pleasing them there. I think people are too focus on how the gameplay is similar rather than all the things that this game offers for Marvel fans. The amount of fanservice and the story are all pretty much something that'll make us feel right at home and everything they complaint has mostly been worked at or going to be worked at, so it's all about waiting really.
I found the review complaining about the lack of characters available to be the silliest one. We've been told a bunch of times that all the NPCs right now are placeholders, and just because they're not playable right now doesn't mean they won't be later. It's a testing period for a reason.