Tom Stoppard, at his best, is linguistic and philosophical fireworks. Watching an ineffective production of one of his cerebral plays, such as the Roundabout’s new revival of his 1982 drama “The Real Thing” (which marks the Broadway debuts of Ewan McGregor and Maggie Gyllenhaal), is not just challenging for the average theatergoer. It’s hopeless.

One of Stoppard’s most successful and accessible works, “The Real Thing” begins with a stiff sort of drawing room comedy scene where a husband accuses his wife of infidelity. Eventually, we come to learn that this was really just a scene from a new play written by the main character, who is about to leave his own wife for another woman.

For the most part, the play is consumed by endless debating over art versus reality, politics, relationships and what constitutes good writing, particularly when the playwright is asked to fix up a poor television script written by a political activist.

Cynthia Nixon, who played the playwright’s teenage daughter in the original Broadway production, is now cast as his first wife.

Sam Gold’s production comes off as vacant and smug instead of engaging. Virtually all its comedic elements go to waste. The Roundabout’s current Off-Broadway production of Stoppard’s “Indian Ink,” though an inferior play, is much better than this.

McGregor makes a solid Broadway debut, and Gyllenhaal has great rapport with him. Nixon, on the other hand, is noticeably miscast, appearing far older than everyone else and having a poor handle on a British accent.

If you go: “The Real Thing” plays at the American Airlines Theater through Jan 4. 227 W. 42nd St., roundabouttheatre.org.