This anthology of Silverberg's favourite science fiction from a period spanning roughly 1953 to 1966 includes a great number of stories regarded by many as genre classics. Some I love, some I love perhaps not so much, but what makes it stand out far ahead from the pack and makes it an absolutely vital addition to the library of anyone seriously thinking about becoming a writer is Silverberg's extensive commentary; every story is accompanied by an essay in which he picks the story apart in order to figure out not only why it ticks, but what it is about the story that makes it so highly-regarded. This makes it invaluable to anyone wanting to write long or short-form science fiction (as a matter of fact, one of the things that decided me to buy it was a review by Joe Haldeman on the book's Amazon.com page which said pretty much the same thing). The lengthy opening autobiographical essay, in which Silverberg recounts the ways in which he obsessively analyzed fiction as a teenager in his drive to become a professional author, is worth the price of the book alone.
There's some great stories in there - Day Million, The Light of Other Days, PK Dick's Colony - and one or two others I can't help but find terribly creaky and old-fashioned, such as Cordwainer Smith's Scanners Live in Vain. Even so, when treated purely as an anthology of sf stories and momentarily disregarding the essays on writing, what you have here is also an excellent overview of some of the most influential science fiction published in the middle part of the 20th Century. Highly recommended, particularly if you want to learn at the feet of one of the grand old men of the genre.