Picnic was very popular with theatre critics when it debuted in 1953, with special notice given to the theme of ordinary people living ordinary lives in small town America. Brooks Atkinson, writing for the New York Times, observed that ‘‘Inge has made a rich and fundamental play’’ from these ‘‘commonplace people.’’ Atkinson found the female characters particularly well drawn and praised the way that Hal effortlessly brings all the women to life. Calling Picnic an ‘‘original, honest play with an awareness of people,’’ Atkinson, also noted that while most of the characters may not demonstrate an awareness of what they are doing, ‘‘Mr. Inge does, for he is an artist.’’

In a review for New York Journal American, John McClain stated that Inge's characters ‘‘are easily recognizable from anybody's youth, and if the author has not chosen to bring them to grips with any problems of cosmic importance, he can certainly be credited with making them powerfully human.’’ Although McClain argued that Picnic lacks the depth of Inge's earlier work, he did note that ‘‘it succeeds wonderfully well in bringing a small theme to a high level.’’

An even more glowing review appeared in the New York Post. Richard Watts, Jr., singled out the work of Inge's director, Joshua Logan, for special praise, referring to Picnic as ‘‘excellently acted and sympathetically staged by Mr. Logan.’’ Watts's greatest praise, however, was reserved for Inge, who he said ‘‘revealed the power, insight, compassion, observation and gift for looking into the human heart that we all expected of him.’’ Watt argued that Inge's writing has ‘‘great emotional impact’’ and that it is Inge's ‘‘capacity for looking into the human heart’’ that gives Picnic its major claim to distinction. As did so many other reviewers, Watt also focused on the characters, especially the women, who he said are ‘‘depicted with enormous understanding and compassion, so that they are not only striking as theatrical characters but moving and genuine as human beings.’’ Watts argued that there is no ‘‘figure in the play that Mr. Inge doesn't seem to understand and see into.’’ Concluding that Inge ‘‘is a dramatist who knows how to set down how people behave and think and talk,’’ Watts stated that the playwright is ‘‘able to write dramatic scenes that have vitality, emotional power and heartbreak. There is a true sense of the sadness and wonder of life in this new dramatist.’’

A few critics focused on the comedy of Picnic in their reviews. John Chapman's review, which ran in the Daily News, called Inge's play ‘‘an absorbing comedy of sex as sex is admired and practiced in a small town somewhere in Kansas.’’ Although, Chapman found the romance between Hal and Madge ‘‘pitiful’’ and ‘‘shabby,’’ he did find that ‘‘Inge has created his characters so well and they are so persuasively acted that they become fascinating.’’ This occurs because ‘‘Inge looks upon them all with understanding, humor and affection.’’ The Daily Mirror's Robert Coleman, agreed, calling Picnic, a ‘‘stirring, hilarious click.’’ Coleman, citing Inge's ‘‘admirable skill,’’ declared that ‘‘it is amazing how well rounded and real all the people are in his play.’’

Negative responses to Picnic were centered on the direction, which William Hawkins referred to as too slick and professional. Hawkins noted in a review for the New York World-Telegram that Logan's work ‘‘sometimes detracts from the heart of it.’’ Walter Kerr, writing for the Herald Tribune, was even more critical of the director. Kerr called Logan's direction ‘‘strident,’’ arguing that ‘‘characters pose, prance, pause, and writhe with alarming mathematical efficiency. Every effort is carefully calculated, planned for the great big boff. Comedy lines are slapped down noisily; the pathos is always conscious of its style.’’ Having reserved brief praise for the setting, Kerr concluded that the performance of Inge's play is ‘‘hopped-up Broadway.’’ Kerr was in the minority among Broadway critics, however, as the majority of them embraced Inge's play, lauding it as a model of modern play writing.