So you want to review a book? Perhaps you could follow John Updike's pointers (first published over 30 years ago):
1. Try to understand what the author wished to do, and do not blame him for not achieving what he did not attempt.Check out the the whole list of rules at Critical Mass.
4. Go easy on plot summary, and do not give away the ending. (How astounded and indignant was I, when innocent, to find reviewers blabbing, and with the sublime inaccuracy of drunken lords reporting on a peasants' revolt, all the turns of my suspenseful and surpriseful narrative! Most ironically, the only readers who approach a book as the author intends, unpolluted by pre-knowledge of the plot, are the detested reviewers themselves. And then, years later, the blessed fool who picks the volume at random from a library shelf.)