Karl Marx was, first and foremost, a product of his time: the time of the first industrial revolution, when the money of the bourgeoisie became more important than the political power of royalty, but everything else remained the same for the people of an increasingly overpopulated Europe still overcoming the effects of the little ice age and the French revolution.
I think the understanding of a man limited to 19th century european scholarship makes for too small a sample to sweep broad conclusions over the whole history of mankind and the experience of civilization, on its various angles and aspects. Certainly it was not enough to grant him the extreme validity to his claims and teachings his followers give him (almost making the man some sort of prophet).
That Marx is still taught on the Humanities, in my opinion, doesn't make him any more valid or truthful. The "social and human sciences" are full of dead european men, like Foucault or Rawls, who wrote piles and piles of ideological nonsense rehashed from previous, greater thinkers such as Rousseau and Plato.
Even for the economic courses and specialisations, it is a shame those who spend time on Marx, given they haven't even discovered Freud yet. And thus are caught with their pants down time and time again when the markets react on seemingly irrational ways and so.
That's really all that needs to be said. He analyzed his world and tried to present his findings as absolute truth that could be superimposed upon any other world. He did not know enough to understand that he did not know enough.
That being said, I think he would be absolutely fascinated by modern society.