This is a topic that could fill a small library (or more!); but in short: yes, classical Marxism is a type of philosophical materialism. It sees human history as a vast system that operates based on underlying, predominately economic, factors; this can be seen by its vocabulary: means of production, modes of production, class, class struggle, value, surplus value, labour, exploitation, capital, bourgeoisie, proletariat, wages, alienation, worker, products of labour, etc. It differs especially from 19th century utilitarian/liberal materialism in that the supreme goal is to achieve a communist society where resources and power are distributed equitably among all people; in contrast to the latter that sees maximisation of personal well being and autonomy as primary goals.
Beginning in the 1970s Marxism was transformed from a materialist philosophy to a metaphysical one through the introduction of post-modernism, especially deconstruction. Deconstruction seeks to derive new knowledge by carefully analyzing semantic relationship within discourses within the context of broader society or a sub-cultures. When applied to Marxism it allows one to substitute in other concepts for class, worker, bourgeoisie, capital, wages, value, etc. Concepts substituted in might be sex, sexuality, women, patriarchy, gender, colonialism, race, disability, and obesity. The chief catalyst of this was the introduction of identity - instead of being a member of a single identifiable, material economic class, one could be a member of multiple classes: white, black, woman, man, indigenous, colonizer, etc. Critical theory was a post modern theory to ascribe moral evaluations to the new relationships created by the above substations into the classical Marxist vocabulary and relationships. This intern creates a moral imperative to correct unethical relationships; in that way Marxism was transformed into a meta-Marxism of which classical Marxism was only one specific applied possibility, i.e. became an idealistic, metaphysical, non-material philosophical system.
Of course, everything in the above is a gross over-simplification, and practically every point would find people to dispute it, but that gives you some idea about the change that took place.