Ellar Coltrane plays Mason, the boy whose life viewers are invited to watch over an extended period of time. He's living with his mother (Patricia Arquette) and sister (Lorelei Linklater), enjoying occasional visits from a father (Ethan Hawke) who was AWOL for a sizable chunk of time, and finding out about life. That's really all there is to it. As the title lets you know, this is about boyhood.
Linklater has always been a writer-director able to create entertaining movies around a core of recognisable truths. That talent is invaluable here, helping the movie to stay far away from the pile of navel-gazing pretentiousness that it could have been. Boyhood pretty much allows you to take away from it as much, or as little, as you want to. There's plenty of drama, and many scenes that people can accuse of having "nothing happen", but there's also plenty of humour, plenty of warmth, and a number of key moments that people will be able to identify with.
Coltrane does well in the central role, which is essential for a film revolving so much around his character. He's not the best actor in the world but, crucially, he always seems quite at ease and natural in front of the camera. Lorelei Linklater isn't quite as naturalistic, although she's perfectly fine in her role. Arquette and Hawke both seize this unique opportunity with both hands, delivering performances that serve as great reminders of their considerable talents. Marco Perella and Brad Hawkins have the unenviable task of portraying flawed men who end up in Mason's life, and Zoe Graham is a young girl who provides him with his first bout of heart trouble (in terms of love, not any medical issue).
I could go on and on about this film. Almost every scene provides some kind of cinematic pleasure. Is it perfect? No. Some of the characters are slightly overdone (especially the one played by Perella), the last half hour feels disappointingly, although perhaps also inevitably, anti-climactic, and the soundtrack, as good as it is, often makes each song feel like what it is - a marker for the passage of time. Of course, those minor failings become even more insignificant when considering the ambition of the film. I'm sure most people will consider me picky for even bringing them up.
This is one of the best movies of the year, I have to agree with the many others who have already said the same thing. It's just not THE best.