Complex sentence: Whispers was probably the most widely respected and one of the most ambitious of the new horror and fantasy fiction magazines of the 1970s, becoming at least as visible and nearly as influential as a series of mostly original anthologies in the 1980s.
Split into simpler sentences: Whispers was probably the most widely respected and one of the most ambitious of the new horror and fantasy fiction magazines of the 1970s. It became at least as visible and nearly as influential as a series of mostly original anthologies in the 1980s.