You might expect “Sessions,” a new musical about eight New Yorkers and their psychotherapist, to be an ironic comedy, something in the vein of an early Woody Allen film or an episode of “Dr. Katz, Professional Therapist.” But the biggest surprise of this lukewarm show is how superficial it is: “Sessions” is blithely unsophisticated about therapy and mental illness.

It’s a given that musicals tend to simplify events and speed up transformations, but great musical theater writers know how to make those rapid shifts feel earned. John Doyle’s Tony-winning production of Stephen Sondheim’s “Company,” now playing on Broadway, offers a master class in how to portray real, complicated people in the heightened atmosphere of a musical without losing any of their authenticity.

“Sessions,” with book, music, and lyrics by Albert Tapper (a venture capitalist by day), works in the opposite way. It takes real people and situations and turns them into life-size cardboard cut-outs of themselves: the battered wife, the bickering couple, the vixen trying to seduce her therapist. Even the set is a caricature: a vast office with windows open to a painted-on view of the New York skyline.

“Sessions” has something of a “Sesame Street” feeling — that sense of the neighborhood types gathering, here in this archetypal New York office. The therapist (Matthew Shepard), has been given the generic name of Peter Peterson, and the patients sport equally unimaginative names. The songs have titles that suggest slightly older versions of ones you might find on a children’s record — “I’m Only Human,” “I Never Spent Time With My Dad,” “If I Could Just Be Like Pete.” And the doctor gives out easy-to-grasp tips like “Dance when you’re feeling down.”

Yet here the “Sesame Street” idea isn’t used to ironic effect (as was so expertly done in the long-running “Avenue Q”). Instead, we watch grown-ups have “aha” moments in a childish atmosphere. There is something painfully unsubtle about watching crotchety old Mr. Murphy realize that he must put his laptop away to resuscitate his marriage, then burst into a soulful ballad with his wife. Or seeing the married Dr. Peterson decide to resist sex with the temptress Leila (who inexplicably dresses like a 1920s dancehall girl).

The story of a therapist who wants to cheat on his wife with a patient sounds like one rife with complications, ironies, and dark humor. But Mr. Tapper’s writing plays them all down, giving us a bland, affable therapist who is sure to do the right thing in the end.

The rampant oversimplifications of Mr. Tapper’s book are even more apparent in his lyrics. A woman about to leave therapy sings of living life “above the clouds,” while a blocked patient says “This is one river I can’t cross.” And Mr. Tapper strains shamelessly to rhyme his couplets (“I’m not concerned with frivolous matters / Like whether I dress in style or in tatters”).

The tunes themselves are merely adequate, the rhythms staid, the orchestrations predictable. There are flashes of something more whimsical and original — such as the Dylan-lite song performed by a patient who idolizes Bob Dylan. But on the whole the songs suffer from the same lack of subtlety as the book and lyrics.

Director Steven Petrillo’s staging and choreography keep the action moving along, and a set of nifty sliding walls works well in dividing the office from the waiting room. The energetic staging masks some of the weaknesses of the material, and the hard-working cast does its best to put across lines and lyrics that strain credulity.

But two hours in Dr. Peterson’s office is a very long time — when Mr. Tapper gives us little reason to care about the trials and tribulations of his therapist-hero. Avoidant, repressive, and strangely detached from reality, “Sessions” is a musical seriously in need of analysis.

Until August 18 (416 W. 42nd St., between Ninth and Dyer avenues, 212-279-4200).