This book may state that the author is "William Atheling", a pen name for Blish. It is attractive for an incisive, cutting analysis of 1960s science fiction. Blish does not go for easy kills by skewering minor authors. Rather, he concentrates on the biggest names of the time, like Robert Heinlein, who was at the height of his fame, having recently written "Stranger in a Strange Land" and "Starship Troopers". Even if you adore Heinlein, it is worth reading Blish's critiques for a deeper view.
Blish also analyses another author who was also a noted critic, Algis Budrys. Here, Budrys comes off better than Heinlein, though his books sold fewer.
Most science fiction fans who have read Blish have mainly done so with his Star Trek novelisations, which weren't even his original works! Here, you can see his skill at analytic deconstruction.