Very strange little experiments, in which the dichotomous form/content model [which I generally find at least to have a certain utility] kind of breaks down. I think the most interesting 'story' is the first of the "three reflected visions" trilogy, where the pure, skeletal vision of wielding -solely- a very specific type of dry exposition [colors, textures, (most elaborately:) the physics of the reflective surfaces], is without exaggeration the entirety of the 'content.'
I think these are true experiments, in that they are not afraid to be duds, and, as in Robbe-Grillet's great cinematic contributions, their aim is to exploit, discover, subvert, our own psychology-- which we have no choice but to experience art through-- and the artificiality of the medium's rules.
However, I think the tools particular to the medium of "Marienbad" [which I consider to be in the top 20 greatest movies ever], and its even greater kin "Man With a Movie Camera" [Vertov, 1929]-- viz. montage, most supremely-- are the tools best suited to Robbe-Grillet's methodology he's using here. So nothing essential, but mildly interesting.