Robert's Stochastic thoughts, formerly Robert's Random Thoughts, summarizes (sends up?) the good ideas in economics as falling in one of 14 categories.
I think he's on to something here, at least if you accept, as I do, that whatever virtues may have lurked in his sociology, Marx was a very poor economist.
Calling Marx a poor economist is a lot like calling Christiaan Huygens a poor physicist. Huygens was wrong to think that space was filled with a lumineferous aether, Marx was wrong to think that all economic value derived from the factor of labor. But it was no more Marx’s fault that he lived before Keynes than it was Huygens fault that he lived before Einstein.
The problem with Marxist economics isn’t that Marx was a bad economist. It’s that so many Marxists refuse to acknowledge that the discipline advanced in the years since his death.
I’m no great expert on Marx, and I haven’t looked at his economics since college, but from what I recall his problem wasn’t that he was born before Keynes, but rather that he followed the French rather than the Scots. Marx was writing somewhat later than Adam Smith. For that matter, Marx was born only 16 years before Walras.