well, i just think this is a superbly interesting book, perfect for dipping in to and re-visiting. If more people were to read this sort of book on trains etc. it would represent a considerable intellectual advance over puzzles and glossly magazines. its NOT a university text book, and to criticise it from that point of view is to mis-understand the aim of the book.
Also, to complain that the consequences of various alternatives are not fully fleshed out is a dire mistake. The book allows a lot of room for the reader to fill in the blanks- for instance, the wonderfully written little segment on the mongols and the death of Ogadai that saved Europe perfectly explains how our continent could have been culturally decimated without trying to piant that particular picture in full.
Another interesting element to that particular story is the destruction of the Caliph of Baghdad by the Mongols. The supreme head of Islam was put in a sack and "trampled to paste" by wild horses. the caliphate has never been restored...how would christians have coped had the pope suffered the same fate?
anyway, questions like that are left to your imagination, which is a pleasant and pleasing thing to get from a book.
the last few chapters are slightly below power, and the over-emphasis on america is slightly grating. But the book clearly believes that the various cultural traits of people can be traced back to historical events- for instance, Russian xenophobia comes from the attacks of the Mongols centuries ago, whilst German aggression is put down to that nation never having experienced Roman rule etc etc. its a highly debatable thought, but to go with it a minute only a young, historically naive nation like America would have the temerity to revise history and re-present it in such an interesting fashion.