CinemaScore is basically an influential exit poll at movie theatres. Despite over 30 years of scores, only 19 films currently hold the dubious distinction of getting an F. Vulture's Kevin Lincoln found a few patterns.
After speaking with research analyst Harold Mintz, Lincoln laid out the patterns he sees:
Most of the straight-up horror films on the list of Fs wouldn't surprise anyone, and for much of the past few decades, those were the types of movies that made up the majority of the form: starlet-driven, teen-oriented schlock that would lure in audiences opening weekend based on stars and serving a need, then give way to the next one. Sure enough, Mintz says that these films tended to deliver low multiples, meaning the overall gross in relation to the opening weekend. This is generally thought of as CinemaScore's main utility: If a movie delivers a poor CinemaScore on opening night, it's a bad sign for word of mouth, and it suggests that a low multiple is likely. If it delivers a high CinemaScore, it's the opposite, and with the higher CinemaScores for horror, Mintz has seen a corresponding increase in multiples, with movies like The Conjuring franchise delivering unheard-of-for-the-genre 3.0 multiples. (Get Out has managed a staggering 5.3 multiple.