As a communist who talks to other communists (admittedly mostly Maoists and 'Stalinists' (which is really a pejorative invented by Trots to demonise Actual Socialism ('Stalinists' are simply anti-revisionist Leninists)), I say that Marxists who apply more than a simple liberal analysis to the USSR would agree that it was in fact socialist.

The Marxists I've known have tended to have the view that the Soviet Union (and this generally applies to Leninism and its descendants and implementations generally) was socialist in both the superficial structural sense (in that it features government control of the means of production and exchange, to a very large degree), and in terms of its propaganda.

Beyond that, there has been less agreement, but many have held the view that the USSR either was not socialism (sometimes referring to it as specifically as "state capitalism") or that it was an approach to socialism, but one which was fatally flawed by (and this is, in some respects, my synthesis of their criticisms, rather than one that was articulated by any one interlocutor) the adaptations to apply socialism without first having institutionalized the bourgeois revolution which precedes the socialist revolution which resulted in property-like (if not formally "property") personal social authority structures which shared features with both the property structures of feudalism which are at the roots of the problems addressed by the bourgeois revolution, and the those of the capitalism that are at the roots of the problems addressed by the socialist revolution, which mostly resulted in the net effect of the implementation of Leninism (and its variations applied elsewhere) being to spread a distorted form of socialist ideology in a society in which elements of both the bourgeois revolution and the socialist revolution were present but where the revolutions as such still needed to occur in the normal order but were arrested (in some cases, less than completely--certainly, even in the mid-1990s, most who held some form of this view seemed to think that at least China was very definitely progressing through the bourgeois revolution) by the identification of the status quo order with the socialist revolution.

Marxist here, I concur. You do have to admit that many people who are new to their studies or people who have a more superficial understanding of socialism often do assert that the USSR wasn't 'real' socialism as a means of distancing themselves from its 'failures.'