This book is definitely not for the casual reader. Printing costs must have caused issues, as everything is crammed in like a tin of sardines! Quite small font, no line breaks for paragraphs and very few illustrations. The sidenote/referencing system is annoying, you have to flip around the book to find the matching number... they are at the end of each chapter, but seeing as everything is crammed in, chapters aren't clearly defined.
Outside the physical publication niggles, Premodern Japan is very informative and interesting. The heian period is boring, but the kamakura and tokugawa periods are well detailed, although the timeline skips back and forth with differing subjects. I have only just reached the meiji period, so I can't comment on that. Currently fervently reading through it in anticipation of an interview at Cambridge less than a week away!
As with any book, your interest will ebb and flow throughout. Someone of the topics are so interesting (and sometimes shocking) you won't want to put it down. At nearly £30, you may want to shop around for a good second hand copy. I unwillingly parted with my money only because it is on the university recommended reading list.