Whitney Houston's voice is without compare, the K2 every R&B diva longs to scale. She's endlessly versatile, growing from ebullient ("How Will I Know") to imperious ("I Have Nothing") and embodying every gradation of skill and emotion in between. For this alone — and the accompanying tons of album sales — her absence from the Hall of Fame is noted. But arguably more important is the late musician's unparalleled role in opening doors for black women: Houston, after years of fighting for respect, was one of the first to receive heavy rotation in MTV's early years, and she is the model for essentially every R&B-pop crossover artist since. "Whitney's voice was so pure and powerful. She had so much control and range and expressive ability," John Legend told Rolling Stone after Houston's death. "We really lost one of the greatest singers we'll ever hear. She was that good. "