Complex sentence: In the 1950s and 1960s, paperback books were rarely reviewed, according to "PW", one of the reviews feature's important innovations was that it made no distinction in the reviewing between hardcover and paperback books.
Split into simpler sentences: In the 1950s and 1960s, paperback books were rarely reviewed, according to "PW". One of the reviews feature's important innovations was that it made no distinction in the reviewing between hardcover and paperback books.