I'm not a huge fan of travel writing as a rule - the 'gag'-hunting of people like Bill Bryson really gets in the way of the actual information about the country that the book is supposed to be telling you about, and most of the time isn't actually amusing. Van Der Post is thankfully not a comic writer, and thus you do learn a lot about Russia in this book. It was written in the 1960s and consequently is of no real use to the traveller today, but is interesting as an historical document - showing how an outsider, as well as many insiders, viewed the secretive and prohibiting Soviet Union and its communist overlords at the time.
The book did drag a bit, notably the parts about Yalta and Tbilisi - again, this is possibly just because of my aversion to anecdotal travel writing that doesn't seem to have any real import - but overall I enjoyed the book and found it illuminating. The author's comparisons between Russia and Africa were particularly interesting, as were his comments on art and artists in Russia, pre- and post-revolution.