Typically, I rave when storytellers try something different. When they stick to the basic three-act paradigm, with flawed characters growing through an arc while fighting through their obstacles, it all tends to be stale, unless it's somehow taken from a fresh angle.
Three Billboards smashes the basic rules. Often it's done in satisfying ways. However, as a whole, it's a hot mess, where the sum is not greater than the value of the often creative pieces.
The story is of a divorcee, whose daughter was raped and murdered. She decides to rent three billboards outside of her rural house to put controversial messages, bashing the local Sheriff for not solving the murder. That's the setup. After that, it's complete chaos for two hours.
Three Billboards excels in moments. The characters are well developed. But not a one of them is likable, except in short moments. In fact, much of the time, you'll dislike every character on the screen. They're just not slightly flawed, they're assault-people-who-disagree-with-them flawed. And they don't evolve much past that ugliness.
Yet, seeing them act like savages does have its moments. In fact, it's charming at times. Though by the end, you'd wish that there would have been more complete arcs. For me, you can create wonderfully flawed characters that you can easily fall for, but if they don't arc, it's just a trip that doesn't seem to go anywhere satisfying. That is the ultimate flaw in Three Billboards. (Along with an absurd coincidence in a key moment that is just horribly lazy writing).
That being said, if you're looking for unique moments, and like watching heavily flawed characters, Three Billboards Outside Ebbing, MO is for you. You have to look past the typical Hollywood stereotyping of flyover land as a place where everyone is a racist, bumbling idiot. You have to not expect satisfying character arcs. You must not be in need of a typical three-act structure. But, if you're into moments that disturb, often very interesting ways, give the movie a shot. You just might like (parts of) it.