A big O might’ve spiced up New Group’s painfully slow production of Kenneth Lonergan’s unnecessarily long play The Starry Messenger, which rambles on through December 19 at the Acorn Theater. But it’s probably a blessing that star Matthew Broderick remains blandly buttoned-up throughout as an astronomy teacher at Manhattan’s old Hayden Planetarium undergoing a midlife crisis and embarking on the most boring extramarital affair ever staged. That said, Lonergan has written some sparkling dialogue and monologues for his friend — all of which were adequately memorized by the time I saw the show, thanks. Broderick’s wife is skillfully played by upcoming True Blood star J. Smith Cameron, who played a lesbian in After the Night and the Music but no longer puts her crazy mom from The Rage: Carrie 2 in her program bio.

Julie White won a Tony for playing a closeted actor’s lesbian agent in The Little Dog Laughed. Justin Kirk from Weeds is celebrated for gay roles in Love! Valour! Compassion! and Angels in America. And Mark-Paul Gosselaar will always be Zack Morris from Saved By the Bell. In one of those fortuitous alignments of the stars, these three bright talents now illuminate The Understudy, Theresa Rebeck’s middling play about the corruption of theater by celebrity obsession, which burns out January 17 at the Laura Pels Theatre. As the frustrated titular character, Kirk rehearses to cover Gosselaar’s action star in a fictional “lost” Kafka play. Playing the harried stage manager, White wrings laughs out of every line and gesture, but top billing should go to Gosselaar’s physique, for which tight blue jeans and snug black T-shirts were apparently invented.