As I type IMDB ranks this as #181 of its Top 250 movies of all time. I didn't like it quite as much as the IMDB raters did. Although it was nominated for 6 Oscars, including Best Picture, it only won one for Best Supporting Actress, Patricia Arquette. (I find that a somewhat surprising win, but I haven't seen the movies with the other nominees.)
Anyway, you probably know the gimmick: the movie was filmed over 11 years (May 2002 - August 2013) with the same actors. This worked pretty well for me. It focuses on Mason, starting when he's seven years old, living with his mom (Ms. Arquette) and bratty sister (Lorelei Linklater, the director/writer's daughter). Mom has split up with bio-dad Mason Senior (Ethan Hawke), but he's still an occasional presence.
So, what happens? Basically, time. Mom gains and sheds a couple husbands (apparently driving both of them to drink, one to physical abuse). The kids do kid stuff appropriate for their age, including sex, drugs, and rock-and-roll. Dad eventually becomes respectable, but not respectable enough to avoid giving Mason Jr. some poor advice about relationships.
It sounds as if it might be boring. Some people have found it very boring. Not me, though, because even though the problems of these four little people don't amount to a hill of beans in this crazy world, I still found them interesting enough to want to know what happened next.
However: it's long (2.75 hours) and drags significantly in the final third. Maybe you'll want to hit the play-faster button on your remote?
I can't help but wonder if they're secretly working on Manhood, to be released in 2025 or so.