I found this book thoroughly absorbing.
It gives an informative look at both communism and capitalism at their most (and least) effective.
Brzezinski has captured the tension applied by and to the American and Soviet governments, militaries and scientists quite brilliantly and tells the story of the political manoeuvrings, technical triumphs and disasters, and social perceptions of the period without getting bogged down in these back stories.
In many ways it reads more like a thriller than an historical account, flipping by chapter from the Soviet side to the American side.
I disagree with the reviews that suggest Brzezinski is biased against the Russians, I found the book to be well balanced. If anything it paints the Soviet scientists as more ingenious (and ultimately more effective) than their unfocussed and technologically arrogant American rivals.
The American reaction to Sputnik's launch is told brilliantly, from the citizens listening to its radio signals, right up to Eisenhower playing golf as the balance of world power shifts under his feet.
The story is studded throughout with finely researched details of the main events from a wide variety of sources, most notably Khrushchev's son, but never loses focus of where the story is going, for example there is a lengthy description about the U2 spy missions but not until the epilogue does it discuss the soviet capture which has become more famous than the plane itself, as it's not directly relevant to the story at hand.
A great account of an epic struggle for technological dominance (or at least the perception of it!)