It’s a Wonderful Life is a heartwarming Christmas classic: A tender movie that avoids being cloying most of the time on its way to causing your heart to sink. It’s hard to go wrong with it.

But also hard to improve upon, as playwright Joe Landry proves in his “Live Radio Play” version, now at WaterTower Theatre. All the elements are there: An aw-shucks dumpling of a George Bailey (Matthew Laurence-Moore), a slimy Mr. Potter (B.J. Cleveland, in one of many impersonations), ZuZu remarking that an angel got its wings. We recognize them all from the movie.

And that’s exactly what’s wrong with this play — it’s not a play. Nor is it the movie. It’s little more than a staged reading, and it begs you to ask: How come?

It begins promisingly: The actors wander through the audience at the Addison Theatre Centre, interacting with them in character as if it’s 1945 and the broadcast is about to begin. The host of the show introduces the actors, and we see the sound effects expert (Scott Eckert), who will give life to the world of Bedford Falls. Then the show starts … and that’s it. Aside from two or three “commercials” and one dropped item that interrupts the action for a split second (it was planned), nothing happens. There’s no conflict, no drama, no off-handed comedy.

Where’s the tension between the actors? Are “George” and “Potter” secretly trying to woo “Mary” — only she’s interested in “Violet”? Is “Sam Wainwright” drunk and has to be replaced at the last minute by the others? Is the sound effects man at his first day on the job and screwing up all the cues? That could make for some antics a la Noises Off, but it never happens.

I think I know why: Landry is far more concerned with maintaining the squishy holiday spirit and being true to the source material than he is concocting an interesting and visual play meant for theater audiences. How simpler it is to let a 60-year-old screenplay do all the heavy lifting, developing characters and such, and not worry with pacing, staging or the like. That’s not writing, that’s typing.

If only the sound man were given a bigger part, or more prominence on the stage, it could have been fun watching him rush around harried while the show’s star (Cleveland again) made his life difficult. Alas, that would have required too much thought.

Not that the actors don’t give it their all. Jim Johnson rolls his eyes ironically to add some humor to the production, and Cleveland does yeoman’s work playing a coterie of characters, each more vocally outrageous than the next. But without a sense of tension, it’s just the movie any of us can see on TV almost any hour of the day in December, without the high school swimming pool scene. What a missed opportunity! Maybe George should have taken the plunge after all.

Plays at Addison Theatre Centre, 56150 Addison Road, through Dec. 16.