Not the worst Beatles book out there, but as a diary it has been hugely superseded in the intervening years by the works of Mark Lewisohn in particular. And it suffers from some glaring inaccuracies and contradictions which make you suspect everything! For example, did Paul join the Quarrymen in 1956 (p12), or in 1958 (p14)?
This wasn't the best Beatles book I've ever read, but it was worth reading. Unfortunately, there was some weird printing issue with my copy and the middle pages were all printed backwards so I had some kind of Magical Mystery Tour to actually read the book (pun intended).