The direction is incisive, but there remains the incontrovertible fact that this is a filmed play that one should have seen on the stage. Failing that however, it is still a magnificent experience to watch Rachel Roberts and Albert Finney reenact on film the union, in George Meredith’s words, of this ever-diverse pair. It is acting at its very highest: anyone who cares a rap about performance penetrating to the essence of humanity owes himself this experience. Watch Finney change from act to act (the movie preserves the act division): he goes from a baffled but still belligerent young husband to a cocky, irresponsible lecher, and thence to a man prematurely old and exhausted but clinging to some illusion of independence. It is not one but three glorious performances rolled into one; I promise you that you have never seen an actor change more drastically without benefit of make-up—bulge out so in one scene, and cave in on himself so utterly in the next. Notice how the eyes go dead, the voice gets blunted, the very outline of the body blurs with defeat. Rachel Roberts is no less superb, but her part has fewer dimensions. Yet how piteously she ages, becomes more thrall to despair, and still preserves a spark of pugnacity, however dulled and enfeebled.
The film simply reeks humanity from every frame or pore: battered, smelly, hopelessly soiled humanity, yet somehow luminescent in its very putrescence.
from John Simon review of Alpha Beta