To me this was a beautifully filmed and chilling movie which was extremely unnerving, in part because, like the people in the film, you don't know what is happening or why, though what you do know isn't good.
From what I have read it is based on the experiences of the writer as a child which (at least to some extent) mirrored those in the film.
It is not a perfect film, there are questions left unanswered at the end, but I think it is still compelling. I do wonder however, if it is perhaps necessary to know something about the "Manson Family" to fully understand the film's plot. Although it is not about the Manson murders or Manson, there are important references and echoes of the mind-set of the Manson family within the film.
For example, it is important to know that "pig" and "piggies" were terms given by the Manson family to others who they saw as targets. Mostly wealthy and white, though not exclusively so.
To "get" a pig or piggy meant to kill them. This is idea is referred to more than once in the film.
Amongst other unpleasant things the family members would do was to "creepy crawl" into people's houses, this meant dressing in dark clothes and breaking in and moving furniture around to mess with the "piggies" minds. Creating terror was a vital part of what the family did.
It is difficult to say anything else without giving spoilers.
For anyone who has a desire to know more about the Manson family and murders (and can stomach it) Helter Skelter: The True Story of the Manson Murders
is a brilliant and factual narrative of the crimes and court case by the prosecutor.