Carlos Valladares’s review published on Letterboxd:
Oh woah. An elegy to and a gathering of the fallen marginal/leftist dreamers of the late 60s; their temporary failure of a dream of elegant utopia is symbolic of a much larger malaise and skepticism present in deranged Western culture that Rivette and his band of actors attempt to pinpoint through improvisation.
Yet, what is Out 1? Quite simply put, there is nothing like it in the vast library. It is a brutal elaboration of what André Bazin could only dream of—a sort of capering-irritating-exciting approach to plan-séquences, long-takes capturing a scene's every shifting mood, deep focus to capture stasis at 3 different stages in the fore-mid-background. It is mixology of the cinematic kind: a lurid mish-mash of dreams and reality, of performance and simply being, of documentary (that is, of this film's own improvisatory making) and fiction (that is, of the fact that there is actually some semblance of a coherent plot that manages to jumble its way out of the improvisations).
This is Cassavetes off the deep-end. These are Godard's theories put into practice. This is an elaboration of what Demy-Truffaut-Godard-Varda-Resnais ideologically stood for: a sort of DIY approach to filmmaking that used the familiarity of friends and the imperfect streets of Paris to create a world more real than reality—and thus more unusual, more bizarre, making for great cinema. This is more frightening than a horror masterpiece, more thrilling than a Superman serial, more heady than a Bergman or Malick chestnut. Often times, it is violently mundane: 10-minute takes of actors going through their rehearsals will not be everyone's cup of tea. But think about what we're watching. These real-life actors are pretending to be characters pretending to be other characters acting normally; then, as the film weasels onward, and as the plot "thickens", as we see these actors outside their theatrical bomb-shelter, we see them accidentally elaborating on what they've learned in their sessions. Mundane, yes, but—this is important to clarify—never boring. Watching Out 1, you get the sense that you're witnessing a grand avant-garde experiment so far into itself that it becomes paradoxically exciting and accessible to watch.
Track down the limited-edition boxset of Out 1 while you can. It demands books of words; and yet, it eludes them, it defies them. Hypnosis of the first quality. Madness takes its toll. The inability to recognize when you're in a "movie" and when you're in reality. Yet if the way we view reality is rather contaminated—Zhaungzi and the butterfly, a spillage happening between the two worlds—what does this make cinema? Rivette, you squirrely bastard, you seem to provide all the answers and yet say nothing that will incriminate you. You let us do the thinking. Bravo.