How (not) to write a book review

I am not a very good book reviewer but I get by. Mostly because I focus on what readers may want to know about the book. But I have edited enough book reviews and attended enough writing and editing courses to know the big no-nos.

Here are some ways to write a review badly

1. Thou shalt write generic reviews.
Over the years I have read some reviews that could easily be used for almost any book. Of course, this also meant that it didn't tell much about the book at hand. When I read such reviews, it typically tells me that the reviewer hasn't read the books. Here is an example of how a generic review may go.
"You will love the exciting text and colourful pictures. Every turn of the page brings new surprises. If you enjoy reading, this book is for you!"

Other ways cheaters review books:
A) Finding existing reviews and remixing or phrasing them into your own.
B) Using a mix of the table of contents and the book blurb.

2. Thou shalt not mention the book.
Amazingly, I have encountered reviews which hardly mention the book. Here's how one may read:
"Parenthood is a joyous time indeed. But every new mother faces incredible challenges of meeting the many needs of her baby. Friends and relatives may add to the problem with their many opinions, causing new mothers to doubt themselves..."
Of course, the reviewer does end with a few (usually generic) sentences about the book.

3. Thou shalt mention things without reference.
"This is an exciting story about three detectives whose parents go missing one day. The children take Timberman and trot the globe on an investigative adventure."
At this point, I'll typically be hunting around to find out what Timberman is. The minor quibble I have is that the fact that the detective were children should have been mentioned beforehand. And are the children siblings? Or Are we talking about different sets of parents? IMHO, this makes for less jarring reading. But I usually leave it as it is a minor point that could pass as the reviewer's style.

4. Thou shalt be ambiguous.
"And so John found his father after much effort. But then he caught pneumonia and died."
Needless to say, it would be better writing to clarify if it was John or his father who died. Unless the next sentences are "So was it John or his father? Read the book to find out." But this is likely leaving the cliffhanger too late. Incidentally, the cliffhanger is probably the most (over)used review technique.

5. Thou shalt not read the book.

Well, that's about all I can think of for now. I've been guilty of 1 from time to time but reading the book has at least been the least I've done. It riles me that reviewers can try to write a review without reading the book. Why do that? Why not just refer our readers to existing reviews? At least that's honest.