It's sort of like "The Awful Truth" as re-imagined by a '50s screenwriter with a smutty mind: Married couple divorce, try other partners, reunite. The high-school-boy-giggling-about-sex tone gets pretty heavy, but try to overlook that, because the film has so much to recommend it: New York location filming, early Kim Novak in a small part, and most of all, Judy Holliday and Jack Lemmon. Was there ever a greater romantic comedy team? She's hysterically funny and amazingly touching at the same time, and he partners her perfectly. They're even sexy together -- it's not a quality you usually associate with either actor. Watch the "mambo" sequence, with their shifting feelings about each other played out in dance: a classic scene.
I'd rate these two over even Tracy and Hepburn. How sad that they made only two movies together.