The travails involved in getting this movie released at all are well enough known by now that the fact that it is a flawed masterpiece shouldn't come as a surprise. Above all, it is a masterclass in how to write dialogue. Virtually every character is given a credible and compelling voice, from the bus driver to the lawyer, from the mother's suitor to Lisa's "boyfriend". As the father of a daughter, now in her early 20's, I can say that Lisa Cohen's character is as realistic a portrayal of the insecurities and self-righteousness of female adolescence as I have seen. All aspiring screenwriters should be forced to watch this movie and then be given a 3-hour oral and written exam before being allowed to put pen to paper (or finger to keyboard).
The acting is also superb. The feel is more of a stage play, an ensemble piece, than a film. Perhaps the fact that one of the characters - Lisa's mother - is a stage actress struggling to support her daughter is partially responsible. But you can tell that this team of seasoned actors relished the opportunity to stretch out with an intelligent well-written script and a supportive director.
The only flaw in Margaret has already been well expressed by others. The film does meander and, while I recognize that this is partly the point of the exercise, there are times at which you long for a more conventional, and taut, storyline. I would gladly have spent more time in the company of these well-drawn, articulate and interesting people. Maybe next time HBO wants to do a miniseries it will let Kenneth Lonergan loose on a story rather than subject us to another preachy, wordy effort from Aaron Sorkin.