Kenneth Lonergan's shattering portrait of a woman's descent into senility is painful to watch, but its heartfelt honesty sets the stage for a very talented company to remind us to cherish the time we've got.

When we first meet Gladys Green, we find a thoughtful, vibrant woman engaged in life and contentedly running an art gallery in the Village that doesn't get much traffic. Her memory is noticeably slipping and she repeats herself a lot.

The play is divided into multiple scenes spanning two years from 1989 to 1991. In between are projected images on a brick facade reflecting Gladys's memories through the years. But with each successive scene, Gladys's dementia becomes more pronounced.

She's funny at first with a wonderfully direct manner, but gradually her lapses and repetitiveness wear thin on the family. Her daughter Ellen, grandson Daniel, and son-in-law Howard are increasingly frustrated with her childlike behavior.

Lila Neugebauer's sensitive direction feels so natural, it's almost like eavesdropping. And while the entire cast is superlative, the show belongs almost entirely to Elaine May's beautifully measured performance. How challenging it must be to seem forgetful, constantly repeating lines while having to calibrate ever worsening senility with each new appearance. And as tough as it is to watch, this is not a maudlin work. It's almost a deconstruction of a family's response to a loved one's mental decline.

Lonergan designed this as a memory play and Lucas Hedges's restrained narration offers welcome distance. Joan Allen wrenchingly evokes Ellen's conflicting emotions. And who can't relate to David Cromer's Howard, with his clumsy but well-intentioned efforts to communicate. And Michael Cera is almost unrecognizable with his subtle turn as a sympathetic artist without a lot of talent.

At one point, Howard tells Gladys, "It's no fun getting old," and Gladys snaps back, "No one wants to hear that." So very true, and yet we do hear it throughout "Waverly Gallery," a play that delivers the hard truth about aging with eloquence and empathy.