Intentionally or otherwise, writer-director Noah Baumbach's acutely perceptive, painfully funny While We're Young plays like a sequel to 2010's Greenberg. In that film, middle-aged crank Ben Stiller was both befuddled and bewitched by a game-for-anything millennial.

This time, Stiller's Josh isn't a single sad sack, but a married sad sack. His career as a documentarian is stuck in neutral, his friends (including a fine Adam Horovitz as a Wilco fan with back problems) are having babies, his celebrated father-in-law (minimalist par excellence Charles Grodin) makes him feel like a failure, and he and his wife, Cornelia (Naomi Watts), are bored.

Things start to look up when the duo meets Jamie (Adam Driver) and Darby (Amanda Seyfried), a couple in their 20s who listen to bad '80s records, watch beat-up VHS tapes, and make all their own stuff. Josh and Cornelia come alive again in their presence—and the movie does, too.

But once Josh segues from besotted mentor to hectoring detective, the tone changes from fizzy to flat and threatens to go off the rails. Baumbach tries to juggle too many themes at one time: the generation gap, the cultural divide between parents and non-parents, and the de-evolution of documentary filmmaking in the digital era. Fortunately, he restores (some) equilibrium, ending on the same funny-sad note—literally, thanks to the music of David Bowie and composer James Murphy—on which it began.

Though critics have taken Baumbach to task for favoring his male characters, the dialogue doesn't bear this out. Darby, knowing she's overshadowed by Jamie, protects her territory by declaring, "We're a package deal." He also makes great use of Watts, an underrated comic performer. And let's not forget Frances Ha, the 2012 follow-up to Greenberg and a deeply sympathetic work about a 27-year-old woman facing challenges the older characters in Greenberg and While We're Young would have dealt with years ago. The result, cowritten by and starring Greta Gerwig, was Baumbach's most perfectly realized film.

It's tempting to surmise that While We're Young doesn't hit the same heights because Gerwig didn't participate (she'll appear in Baumbach's next effort, Mistress America). The problem could simply be that Baumbach is too close to the material to know when to pull back.