I've often been asked what I look for when I review a mystery. At first, I thought there was no way for me to do that, because my decision depends on how I feel about a book.
But let me try to take you through my process and see what happens.
Another thing that turns me off is a large number of characters, especially if they are similar. Agatha Christie’s Death on the Nile or Murder on the Orient Express each have a dozen or more passengers who figure in the story, but their names and occupations vary enough that there’s minimal confusion.
If a story requires a large number of characters that could be mixed up, a cast list at the beginning or end of the book helps a lot. I have not reviewed (and sometimes not even finished) books in which I couldn’t keep track of who was whom.
Too much technical detail is another problem. I’m a librarian, and if I don’t know something, I know how to find out about it. But I’m not going to enjoy a book if I have to keep looking stuff up. Medical and legal mysteries that focus on a complex procedure rather than how they affect characters, relationships or plot don’t hold my attention.
At the same time, I’m not a sycophant. I do try to make my reviews positive, but if there’s a little thing that bothers me, I will mention it, along with the fact that it is just my opinion.
Because, in the end, a review is nothing more than one individual’s reaction.