I've read parts of Das Kapital and I have read a bit on Engels. Wasn't jhe the one of the first to pimp the idea of using public education, the right to education, to indoctrinate the masses into Communism?
He was saying that by educating workers they can realize their own self interests and better assert themselves on a equal level. He is correct also. Education is the key. If you are for example in a foreign city it is hard not to be ripped off, as you do not speak the language and may not understand currency exchanges or the finer details of a contract. (my apologies for poor analogy I am going from the top of my head from DK)
Really I read Engels as basically a anti-trust framework. It's not really anything controversial in the modern world of labor disputes.
The whole "communism" rhetoric was a way of gathering an idea to words, it was crazy folks like Lenin decades later who took the concept of "dictatorship of the proletariat" to mean big government.
Even Marx said this is not what it is about. (Which is where the quote from Marx comes in: "If this is Marxism then I am no Marxist!")
Now, if you would like to criticize Marx and Engels from a traditional Socialist standpoint back then (1850s-60s) I would recommend Bakunin, he was their nemesis. (the libertarian socialist wing)
Marx and Engels scientific studies of dialectical materialism is still relevant, moreso then ever actually.
The whole philosophical rants in Manifesto about "workers uniting under a tyranny of democracy" sounds like he came up with it while studying the finer aspects of social sciences drinking vast quantities of wine while having a few ladies on his lap at about 3 am. But then..that's Comrade Karl for ya.
This is from a few years back, but I think old Marx would dig it.
http://www.youtube.com/watch?v=ivjuAPs9pYA