So what is a “transformative” use? If this definition seems ambiguous or vague, be aware that millions of dollars in legal fees have been spent attempting to define what qualifies as a fair use. There are no hard-and-fast rules, only general rules and varied court decisions, because the judges and lawmakers who created the fair use exception did not want to limit its definition. Like free speech, they wanted it to have an expansive meaning that could be open to interpretation.
Most fair use analysis falls into two categories: (1) commentary and criticism, or (2) parody.
The underlying rationale of this rule is that the public reaps benefits from your review, which is enhanced by including some of the copyrighted material.