Depending on the author's purpose, a book's realism, or truth to life, may need assessment. If a book of fiction is meant to be realistic fiction-is it? Is it logical, natural, plausible? To what extent does the author rely on coincidence or accident to propel the plot? Is there adequate evidence of character motivation? Or a lack of sufficient urges and drives? Is the story infused with a quality of normalcy, or abnormality? Remember, if a book of fiction is to be successful according to a reviewer, it is not necessarily realistic fiction; a book's realism, or lack thereof, need be addressed by a reviewer only as it compares to the author's intention for the story.
See here how David Milofsky addresses the realism of William Trevor's novel The Story of Lucy Gault: "It seems unlikely, to say the least, that longtime residents of a place (going back several generations, we're told) would cut off contact so completely as the Gaults do, but, of course, if this isn't the case there would be no novel. Similarly, it's hard to believe that the lawyer wouldn't be able to contrive a way to contact the absent parents . . . It's a tribute to Trevor's genius that these objections are largely overridden and storytelling takes over."