It seems like the people complaining about it have a few major themes that are common:
- No jump scares (so in their minds, not scary)
- Predictable twists
- Romance was pointless
So I think the issue is not that the show isn't good (because it seems to be getting pretty great praise everywhere but this forum), it's that people expected a modern-style horror show/movie, and got a gothic fiction/romance instead, and don't like it
because of that, even if the content is good. Kind of like if True Detective 2 had actually been Band of Brothers. A fantastic show, but not southern gothic mystery. I get that disappointment, but I also think many are overlooking the great quality of Bly Manor because they didn't get jump scares, or they were able to predict things (that personally I don't think were meant to be that secret, the groundwork for the "twists" was laid out fairly well).
I think, overall, the show is a great experience, and I enjoyed it for that.