Just got back from seeing this movie.
It is a good, not great, movie. The best features of it are that you really get to know the characters and the dialogue is very much like eavesdropping on real conversations. The acting is excellent throughout, with the unfortunate exception of the main character, who becomes pretty flat and monotonous once he hits high school.
As someone said earlier, the movie is as much about the parents as it is about "boyhood."
Two scenes stood out for me. First, the scene later in the movie when Mason's mother has married the veteran and his father and new wife and son have come to pick up Mason and Sam. There is a sense of forgiveness and healing among all the separate factions which is very nice to see, although, as we learn, it does not last.
But the best scene for me was his high school graduation party. It perfectly captured Mason's awkwardness at such a fuss being made over him and the pride his parents have, and also did a fine job of showing the still-awkward relationship between Mason's parents.
This did not spoil the movie for me, but I do want to point out that there are three scenes that are explicitly left-wing politics: Ethan's father launches into a rant against GWB and the Iraq War; Ethan's dad, Mason, and Sam are putting Obama signs in people's yards, and the person who objects has a Confederate flag in his carport (opponents of Obama, as we all know, are racists!); and much later the vet says that the war was "all about oil." It's just so tiresome.......
The casual drug use of magic mushrooms at the end was a bit jarring, too.
It's worth seeing.