3. Inappropriate Rock
Grand, sprawling manors; thick fog; imposing trees; ominous shadows; and a rock soundtrack? The musical choices for this film are atrocious, and anyone with common sense could have known how awkward it would feel. The only reason for this creative decision must have been to ground the story in the 90s; the film even kicks off with a news story about Kurt Cobain's death.
While there's nothing necessarily wrong with the modern setting (The Haunting of Hill House, for example), we don't need it drilled into us with the soundtrack. It's very distracting. They seem to forget that it's moody, Gothic atmosphere they're aiming for.
There's also a cringe-worthy scene involving Finn Wolfhard and a drumkit that we probably could have survived without.