Disclaimer: I received a promotional copy through the First Reads program. So a tip of the hat to Random House.
Note: The edition I received was a 304-page uncorrected proof.
Macintyre did a good job with this one. His writing is accessible. The book moves at a good pace. It is packed with information, and quotes from first-hand sources are frequent. There are humorous anecdotes, as well as accounts of covert field operations. The Afterword, by John Le Carre, is mostly notes he took from a 1986 interview of Nicholas Elliott.
While Macintyre handled the subject well, one can not escape how depressing the subject is. It's essentially 300 pages of horrible stuff happening. Philby might be the main focus, but the underlying theme is the damage caused by English arrogance and incompetence. There's no way to undo what was done. There's no happy ending.