The New York Times says,
“Three Billboards” is more ambitious than Mr. McDonagh’s earlier features. Like the older ones, it has loads of gab, plenty of guns and the spectacle of men (mainly) behaving terribly. ... This time, though, he has also given his movie characters instead of disposable contrivances, a plot instead of self-reflexive ideas about storytelling and a rather diffuse overarching metaphor. Mostly, he has freighted it with a tragedy that allows the performers — primarily Ms. McDormand but also the equally excellent Mr. Harrelson and Sam Rockwell — to play to their range.The New Yorker review made me wonder if they'd watched the same film I had. The Atlantic opens with this: "Featuring standout performances from Frances McDormand, Woody Harrelson, and Sam Rockwell, the writer-director Martin McDonagh’s latest is one of the best films of the year."
The Telegraph gives it 5 out of 5 stars and says, "Martin McDonagh's gut-twisting comedy will make you stand up and hoot." The Hollywood Reporter says, "The performances could scarcely be better". Variety says, "Mostly, the movie takes the new war dance of feminine righteousness and masculine power and holds it up to the light in a nearly mythological way..."
Rotten Tomatoes has a critics rating of 92%.