Sadie's subplot with her former best friend and the "high school mean girls" crowd felt a little shoehorned and ended up unresolved completely. The film's runtime topped just over 90 minutes so it's difficult to add in too many plot threads. I also felt all of those characters were just tropes, and not one I enjoyed seeing and not ones that felt self-aware.
I really would have liked to see more subtle, psychological horror in this. Considering it is PG-13 and a bit bound to not show blood and gore, though it implied the death of a very child early on that's about it as far as boundary pushing went. Boogeyman is supposedly a monster driven by grief and seems to possess an array of different powers and abilities; I'd have liked to see something like they did in the IT movies with Georgie; some on the screen stuff and can give you a chill. Perhaps they were being true to the source material (I haven't read it) and maybe doing that would have made him too much like Pennywise, but yeah.
All that being said, I consider the films I put into my B tier to be good movies. I'm not a terribly hard to please person when it comes to movies usually, so I would say I like things more often than I dislike them. B tier films are ones I would say I recommended seeing, but that they may have some flaws here and there to stop them from achieving greatness (in my opinion, at least). C tier movies are the sort of "take it or leave it" kind; they're not bad, but you aren't missing out by missing out either. Stuff below that I would recommend against seeing, of course.