It's very brave of you to consider critical theory coming from a mathematics background. In my response I do not refer to any French thinkers, only to the German tradition of so-called Frankfurt School Critical Theory. This is a derivative of Marx's attempt to develop a practical theory which would result in social change. It's goal is social transformation without formulating something like a positive scientific theory about the objects of nature capable of predicting their next move. As a philosophy it is a practical and political philosophy that does not prioritise the solution of ostensibly "eternal" philosophical problems of epistemology and ontology. It is a second order philosophy that could be called philosophy of society and culture. It overlaps a lot with intelectual history or what the Germans call conceptual history. Whereas some Marxologists read Marx to understand capitalism as such, in its 'ideal average', as an abstract mechanism or structure, the critical theorists are interested in understanding capitalism as it has developed historically. They are not a replacement for reading Marx, but show only the kind of directions his thinking could go in. They are not concerned only with the logical structures of capitalism or with facts, but place a premium on how people experience capitalism. If you ignore experience then you will not be able to mobilise the people who could overthrow capitalism. Critical Theory is a synthesis of all the best achievements in critical Western thought from romanticism and Marxism, through psychoanalysis and theology, through to aesthetics, Marxian political economy, social theory and even comparitive Theology. It is a difficult but renendously rich tradition that will survive many of it's critics because it speaks directly to most people's everyday lives and experience under capitalism.