★★★★★: I loved it (even if I don’t know/can’t explain why) and I absolutely recommend it.
★★★★ : I really liked it and probably will recommend it.
★★★: I thought it was good. Not great, not awful. If it’s the first in a series, I might read on. I would probably recommend it.
★★: It wasn’t really for me, but I probably would recommend it to people whose reading preferences I think it would suit.
★: I really disliked it/hated it and do not recommend it.
Sometimes, I just love a book, even if I also recognize problematic elements within it. If I had a good time reading it, and it felt like a 5 star book for me at the time, that’s what I’m rating it.
The same applies to any rating I give a book, but I do try to explain what I liked/disliked when I review the book.