The story was very nice, but the writing's cheap/obvious execution ruins it. There is a famous saying that originates from Anton Chekhov that is commonly used in film schools: "show don't tell." This picture breaks that simple saying in almost all of its lines, as characters will just randomly blurt out how they feel - all while keeping a neutral look on their face.
Baumbach has also made a living out of his quick wit and intellectual humor, but unfortunately in "Mistress America," he decided to throw intellect out the window.
There are a few redeeming factors: its Woody Allen-esque use of camera-work, fitting choice of music, and easy to like characters.
Though it doesn't live up to his previous films, "Mistress America" should be watched by Baumbach fans. If you don't like him, you won't like this; and if you haven't seen his other work, I recommend you watch that instead.