Rothbard's argument is somewhat vitriol, he uses ad hominem extremely freely without realizing that it distances him from the reader. Ignoring how many times Keynes is described as a terrible and malicious figure (perhaps George Lucas based his idea for Palpatine off of this text) I find the style of criticism interesting.
Although quite long and sometimes a bit dry, Rothbard greatly explained Keynes (albeit with much bias) before launching his actual criticism. The information set fourth created a picture of Keynes that was both very egotistical and manacle, it almost seems like Keynes was "playing" with economics to watch the lower classes react.
I found that his personal separation being the root for his fascist beliefs was the best defended argument. Things like the fact that Keynes would define himself as bourgeois and his historical agreements with figures such as Mussolini and Oswald offer a nice comparison for thinking about the Road to Serfdom. The criticisms offered in the latter sections reinforce my beliefs in the correlation between control and fascism.
In the end Rothbard's use of derogatory terminology was not necessary but he was at least being honest in pointing out he did not like Keynes. I would not however suggest this text to someone to teach them about Keynes.