If you "get it", it's magnificent.
If you don't, it's decent.
Please understand that "getting it" does not necessarily mean you've gone through a school shooting. There is so much more to this movie that, at times, the school shooting becomes insignificant.
Above all, it's a movie about acceptance, both superficially--of a traumatic event, but also of people who are different for whatever reason.
It's also a movie about unendurable pain, and how different people endure it. In this case, the contrast between Alicia's rage and Deanna's obsession creates an atmosphere of such palpable anxiety that halfway through the movie we wonder how the director could possibly pull a happy ending out of his hat. Thankfully, the audience is given credit for being human beings; our intelligence is not insulted by a sappy, implausibly moralistic ending.
Above and beyond that, I try to keep a clear head about movies being fiction and all that. Yet I must admit, I cried like a lost little baby during this movie. There were certain things about it that hit *very* close to home and opened up some old wounds that never quite healed. But that is not necessarily a bad thing.