"Felix" (Jack Lemmon) and "Oscar" (Walter Matthau) are close friends who regularly meet with others to play poker and chat. Their bond faces a challenge when one of them reveals he's separated from his wife. "Oscar" steps in by suggesting the friend move in with him, leading to a sequence of amusing situations as they navigate living together. It’s evident early on that “Oscar” isn’t particularly tidy, and their relationship begins to show strain as the story unfolds. Neil Simon crafted some sharp, funny dialogue which both actors perform with impressive ease; they fully embody their characters—an uncommon setup for two men—and provide a captivating look at how these friends struggle when forced to live together constantly. Apart from brief appearances by their poker companions and an awkward double date involving sophisticated British women “Gwendolyn” (Carole Shelley) and "Cecily" (Monica Evans)—which comes after a scene of frustration about lateness and meatloaf that many will find familiar—this is a testament to the chemistry between two performers. I believe, surprisingly, this could be considered a love story. Not in a traditional, romantic way, but despite their arguments and disagreements, these men clearly have affection for one another. The theme song is quite nice as well.

Source on TMDB