Whatever anti-war cachet this much-feted film had in the days of the Vietnam War (Altman suppressed all reference to the original setting of the Korean War but 20th C Fox insisted that it be re-introduced in the film's prologue) has long since evaporated whilst its comedic style, being little more than a series of sketches, was in many ways better suited to the small screen format of the hugely popular television series that followed it and which has effectively sucked the life from its progenitor. As for the supposed humour, I've always found the sophmorically absurdist irreverence of the film's "heroes", Captain Hawkeye Pierce (Donald Sutherland), Captain Trapper John (Elliott Gould), and Captain 'Duke' Forrest (Tom Skerritt) as they take endless potshots at their nitwit colleagues (including the mis-cast Robert Duvall as Frank Burns) more irritating than amusing and the deadpan delivery in an essentially plotless film devoid of character development less than engaging.
Released the same year as Mike Nichols Catch-22, which given the enormous popularity of Joseph Heller's source novel unexpectedly stiffed, it was the first box-office success for Robert Altman who made much use of what was to become his signature improvisational style. The director largely jettisoned the Ring Lardner, Jr. screenplay, based on the novel by Richard Hooker, that nevertheless won it its only Oscar.
BTW: M*A*S*H* stands for Mobile Army Surgical Hospital.