In fact maybe the book is a bit too easy to read - I felt that the reader isn't really challenged with the counterintuitive nature of Einstein's ideas. Hence it is probably best as an introduction to Einstein's ideas which the reader can follow up on. (there are notes and a list of further reading at the end but surprisingly no index)
In the last three chapters of the book we find out about Einstein's quest for a unified field theory, where Kaku point out how his ideas were forerunners of today's 'theories of everything'. We also hear about Einstein's his battles with quantum theory where I felt that Kaku could have stood up for Einstein more. I suppose the majority opinion amoung physicists is that Einstein was wrong in these battles, but that's certainly not my opinion.