Marxism can be another kind of metanarrative:
a) It explains everything in terms of a grand story about the history of modes of production, the nature of progress, the alienation that results from that;
b) it is based on the rational self -- we can understand the world and find our place in it by understanding the economic basis of human activity;
c) it legitimizes certain revolutionary behaviour in the cause of the emancipation of workers; it defines what is true and what is false, what is good and what is bad;
d) it is abstract, in the sense that it appeals to dialectical materialism and the nature of progress. It is, in this sense, ideology, even though Marx hated the term.
e) It is emancipatory -- if capitalism is overthrown, the worker's problems will disappear. There is a clear salvation within the theory itself.