A friend of mine calls this "The Horror". It is in the very application of Marxism that the whole thing falls to pieces. I think Marx was great at analysis, however he didn't understand work or the layers of design and engineering that lies behind the means of production. Also, he was a theorist whose ideas got applied while he was still tinkering with them and pretty much all of his ideas of how to solve the problems he had identified were pretty terrible. The economic questions he posed however, have still not been satisfactorily answered.
> I've heard Marx described as having been great at diagnosis, but terrible at prescription.
Marx and Engels weren't all that bad at prescription -- a substantial portion of the 10 key concrete policies for "advanced countries" in the Communist Manifesto have been widely and successfully adopted in the modern, developed, "capitalist" world.
Lenin's rewriting of Marx's program to a very different one, with notionally the same end state and, in many cases, similar near term policy changes to be applied in very different contexts, that was supposed to work in conditions which had neither the specific problems Marx's program was designed to address nor the foundations from which Marx's program was designed to address them, hasn't worked out very well, but that's a different issue.
