Good: A thorough presentation of the events leading to war, and the ideologies and personalities involved. A good overview to non-initiated. Although there are other books written with similar reach, most of them have been written before the opening of Soviet archives and are thus deprived of some important sources.
Bad: A somewhat chatty writing style, not very useful maps. A couple of gross factual errors regarding the Finnish participation in the conflict left me doubting the accuracy of the entire book. Bellamy takes the estimate of Finnish casualties in the Winter War from Soviet sources, and based on that hardly neutral source he claims that almost twice as many Finns were killed in that war as very thorough Finnish official statistics say (Russians say 48,000 and Finns 26,000). The name, date, and the place of death is known for almost all Finnish casualties, most of the bodies were brought home for burial, and there is no way 22,000 extra deaths could have been hidden.
Bellamy also says that in 1941 there were 150,000 Finnish troops mobilized against Russia, when in fact general mobilization had almost been completed by June 22nd when Russians airplanes attacked Finland and by July Finland fielded 470,000 troops (from a population of 3,7 million).