It is a good book in the respect that Johnson treats the Jews favourably in many ways when looking at history.
On the other hand, his grasp of the Jewish religion is not that great, and is tainted by his left-wing beliefs. In talking about certain religious issues, he takes certain passages out of context; as wll, he holds to the modernist academic view of the Rambam, which is quite inaccurate, and heavily based on ideology.
Nonetheless, I found it to be a very good book, and even though he is a bit of a lefty, Johnson is an author who respects the JEwish people and what they have done.