for example audience reviews from "Saw IV" reflect the opinions of people who are already inclined to go see movies in the kidnap-torture-dungeon genre
Even if I was into that genre, since I haven't seen Saw 1-3 I doubt I would see the fourth installment of a franchise without knowing the characters, etc. I would start at the beginning. I am not into superhero movies, but given the reviews I might give BlackPanther a try but I would probably wait for the DVD.