If you have read issues of Unknown/Unknown Worlds, you know what a superb magazine it was. Stefan R. Dziemianowicz writes about every story that appeared in the magazine's much too short run, from 1939-1943. This is an amazing (and well-deserved) tribute to Unknown.
I must add that my brand-new copy of the paperback edition literally fell apart the first time I opened it. The book merited a better fate.