I'm torn on this book, and my ambiguity towards it can mostly be explained without even referring to the actual contents. Let's get that out of the way first, then.
Critique of Economic Reason thinks it's post-Marxist because it combines Marx with Weber and (strangely) Freire, seemingly deepening and broadening terms that Marx only used in an economic dimension. In actuality, Gorz is post-Marxist because like Adorno, Marcuse and others, he likes Capital and the Grundrisse and conveniently drops out all of Marx's (and marxists') other writing, and with that fundamentally erases (if not flat-out denies) the insoluble contradictions of class and capital. The battle for shorter labour hours (which, don't get me wrong, is a critical part of communism at a certain point of the development of the means of production) is framed entirely as a battle to be fought by trade unions within the framework of social democracy and, by eschewing any reference to direct action, organising, militancy or revolution, is perfectly congruent with Laclau & Mouffe's theory of societal change via hegemonical struggle. This may be a consequence of the 1950-80 period, during which the welfare state seemed stable enough to nullify class contradictions.
Having said that, Gorz' ecclectic writings did produce theoretical value that can operate outside the book's framework. I'm thinking here specifically of his research into the composition of the German labour force, ordering the subclasses by occupational stability, degree of necessary schooling and mobility between firms. Another rock-solid chapter is that on women and the role of the family within the labour force; within it, he develops a strong argument for why 'housewife' should not become a state-subsidized occupation (as this would amount to paying women to stay indoors) - the solution would rather be to, again, lower the hours of waged work (without reducing wages) so as to free up family time for both partners. This should go with the caveat that the relevance of this argument hinges on whether or not society is progressing towards socialism or whether we should make temporary accommodations in the knowledge that the need for them must still be abolished. Gorz' delineation of the specific non-economic nature of certain occupations such as doctors, therapists and prostitutes is likewise interesting with regards to the practical implementation of socialist policies.
I'm mostly indifferent towards the first half of the book, where Gorz in an exercise of immanent critique demonstrates why work hour reduction is necessary. Marx already tells you that, and I fail to see how the additional views of a varied bunch of philosophers and thinkers adds to the substance of the arguments, especially seeing as the self-professed phenomenologist Gorz partly relies on thought-structures that in Marxist parlance could only be described as idealist. For instance, his assertion that 'autonomy' (as part of the new and improved autonomy-heteronomy axis complementing Marx' freedom-necessity-axis) in working life can never be achieved if dependent on machinery (due to the fact that machines are governed by their own laws-for-themself and thus 'heteronomously' turn workers into extension of the machine-process) seems to me to be the type of techno-fetishistic confusion Marcuse too falls prey to: as Marx pointed out, the forces of production derive their nature from the social relations within which they function. The hoe (or for that matter the sickle) may 'phenomenologically' appear as a much more neutral non-heteronomous tool than the furnace, but they likewise impose limits and requirements as to what can be achieved with them and what needs to be done to utilize them. Turning away from the hoe without either replacing it with a different tool in a different sector of work or forgoing tools altogether and living in paleolithic conditions are only possible if the worker leaves the social system completely. Furthermore, from a marxist or political-economic point of view they are identical: fixed capital multiplying the productivity of living capital. [EDIT: this was a bad take on my part; the main difference between machinery and tools, of course, is that as means of production the one is owned by the producer while the other must necessarily be in the hands of the capitalist, and it is this distinction which leads to autonomous/heteronomous practices]
All in all, Critique of Economic Reason is okay but bits of it are built on theoretically shaky grounds and must be read as such. I especially have doubts about the continued relevance of this type of ‘post-scarcity’ personal-preference social democratic Marxism due to the terminal prospects of this system in the near-to-midterm future. Glean from it the snippets critically analysing liberal co-optation of socialist efforts but keep his own professed socialism at a distance.