Scott Greer is brilliant in Arden's 'Every Brilliant Thing'

"I bet they don't do this at TouchTones!" said Scott Greer. And he raced around the room and high-fived the entire (well, nearly) audience of about 80 packing the brand-new small stage upstairs at Arden Theatre Company's Hamilton Family Arts Center. He'd just shouted out, "Sex!" and got all to raise hands for high-fiving.

TouchTones is a big musical running downstairs and a few doors down on the Arden's main stage. They ain't high-fiving everyone down there. But upstairs at the "Bob and Selma," they're doing Every Brilliant Thing through Dec. 10, and on the Bob and Selma you can do things like that. It's the inaugural production at this upstairs space, and as Arden cofounder (and Every Brilliant Thing director) Terrence J. Nolen said before showtime, it's for "experimentation, new things, the unexpected."

Every Brilliant Thing is an audience-participation heartbreaker. It asks what we all ask: What makes life worth living? As a little boy grows into a man, by fits and starts he creates a list of every brilliant thing. Item 1 is, of course, "Ice cream." Item 777,777 is "The prospect of dressing up like a Mexican wrestler." (Not the actual doing of it; the prospect!) And "Sex!" is on that list – thus the delighted, over-the-top, racing around the room.

Greer, a gifted comic actor with decades-long Arden ties, has the energy and improvisational chops to turn this one-man-show into a cast of 80. You should see him work the room beforehand, looking into people's eyes, schmoozing, giving instructions. Few realize the play has already started. If you go, be ready to be a father, a teacher, a school counselor. Greer's ad libs rock. He walks arm-in-arm with an audience member playing a girlfriend (brava her!), and as he releases her back to her seat, he says, "We'll kiss later." One man has a U.K. accent: "This guy watches Masterpiece Theatre, I bet." When a man playing a teacher corrects him on the pronunciation of Goethe and Werther, the audience roars. He's got 'em.

Greer uses fun to focus us on each item on this all-important list – and on uncertainty, loss, suffering. The brilliance of Duncan Macmillan and Jonny Donahoe's play is that we come to depend on that list and those brilliant things. We revel in the word plinth and the voice of Nina Simone and the backbeat of "Get Up Off Of That Thing." Sure, in the play much depends on this list; it's everything to the boy-turned-man. But the larger facts – that these are brilliant things, that hope depends on knowing and loving them – make them ours as much as his.

I saw Donahoe do this play, tremendously, at the Edinburgh Festival in 2014, and I admire how Nolen, Greer, and company have Americanized it, how Greer's physicality – on and off at will, charging round the room one moment, paralyzed and deflated the next – makes it his own. And ours. We come away with more love for life. Add this play to the list. It's a brilliant thing.

Every Brilliant Thing. Through Dec. 10 at Arden Theatre Company. Plays at the Hamilton Family Arts Center, 62 N. Second St. Tickets: $37-$55. Information: 215-922-1122,  ardentheatre.org.