Best to start by saying this is not a true biography. We learn very little about the good doctor from this book: no family revelations, no grasp of whatever theology he subscribes to (he obviously does have some theological standpoint as anyone who has read his work on the Exorcist alone would see), no insight into his personal life. No, this is certainly not a biography in the usual sense. What you get here is a life told through the movies that Kermode has viewed, the people he has interviewed, together with the places he has visited and the jobs he has held that relate to "the movies".
Is this a bad thing? I suppose that depends on what you expect. Do you care when he lost his virginity, who he has shagged, what his political views are (we learn much of what they were in his youth), what lead him to study his Doctoral thesis, his relationships with his wife and children, why he changed his name to his mothers maiden name after she divorced and even worse his thoughts on Simon Mayo? If you do, give this a miss - and then try to get a life. If you don't care about these things, but just want more of the sort of thing Kermode talks/writes about on either his blog or with Mayo (god help you) then this book is fine and you already know what to expect
In simple terms, this is a good book on movies and movie makers, or at least it is if you enjoy, or are at the very least entertained, by Kermode's reviews and radio show - and his rather idiosyncratic take on these. If you enjoy these then you will enjoy this book. And if you don't? Well, you probably wont be looking at this review in the first place.
By the way, take a look at the audiobook also if you get the chance. It's read by Kermode in his usual style and adds something the written word can't. Buy both, I did. Have to help pay for all that hair wax he uses after all.
PS: Have to agree with the dead Python below mind: the cover on the paperback edition is crap.