I've not read any others in the "great philosophers" series but I have read a few of the "x in 90 minutes" and " on x" series (very similar in that they run about 70 pages each and are meant to serve as brief layperson's overviews). From what I know of this type of book, this one is quite badley done.
As a long time fan of Popper, I sympathize with how Mr. Raphael must have felt in attempting this project. Karl Raimond Popper was a thinker whose ideas lead him from and to many topics. From ontological speculation (realism) to epistemology (critical rationalism) to the progress of science (conjecture and refutation) to ethics (a very bizarre and unfortunately not so discript pragmatic liberal humanism) to politics (democracy with again, not so discript piecemeal engineering). If you read his autobiography "An Unended Quest", he even has a philosophy of music!
For all that, Mr. Raphael could have done 10 times better than he did. Out of all the ideas above, Mr. Raphael talks about only conjecture and refutation (in 10 intro pages that compares in attitude to a kid being forced to eat her brussel sprouts).
The next 49 pages are spent discussing Popper's views on the impossibility of historical prophecy. Not that these views arent important but in light of Popper's humongous contribution to the philosophies of science and epistemology (and the non-contriversial nature, at least in todays world, of Popper's anti-historicism) focusing, by in large, the whole book on it is putting pages to bad use.
What caused me, though, to give the book 2 stars (I may have given it 4 otherwise) is that the book is marketed as an introduction to the ideas of Popper for those who've either never heard of him or never read of him. Had this book been marketed as an intro specifically to his anti-historicism, it would have been much easier to swallow. As it is, the reader taking this as an apropos introduction will be infinitely misled.
Fortunately there are better introductions. Bryan Magee's "Philosophy in the Real World: An introduction to Karl Popper" is, with maybe 40 more pages than this volume, a much better, more accurate, and proportional volume written by someone who knew Popper as a teacher and friend. For the student who has more time, Geoffrey Stokes "Popper: Philosophy, Politics and the Scientific Method" is a book that examines, first, Popper's political philosophy and works backwards to reveal how his philosophy of science gets him there. The best introduction, however, is going to be Popper's own "In Search of a Better World".