Moon's musical importance was similar to that of Brian Jones in the Rolling Stones. In much the same way that Jones, through his talent (and his abuse of it) helped lift the Stones above the level of every other blues-based band going, and made their image distinct, Moon did the same thing for the Who. When Jones left the Stones, to die just a few weeks later, they became more professional musically; they settled down with a true and admirable virtuoso in the guise of Mick Taylor, and their sound tightened up, but the youthful edge, the teenage lust was gone, not only from their sound but from their playing. When Keith Moon died, the Who carried on and were far more competent and reliable musically, but that wasn't what sold rock records.
Moon occasionally played on other peoples' records, but he only finished and released one solo album of his own, Two Sides of the Moon (though another may have been planned in 1975). Not taken seriously at the time, this record now appears to have captured the essence of Moon's nature. Recorded in a series of marathon sessions that were as notable for their huge bills for alcohol as the studio time involved, it is a strange, haunting mix of innocent '50s/early-'60s rock & roll and leering, joyful lust, and a savage sense of wit directed at the music business and played out both between and in the songs themselves. ~ Bruce Eder, Rovi