Feeling that in Popular music (non-classical), the melody and vocalist are my number one priority (I am hesitant to say that, as it may seem to minimize my love of harmony and counterpoint, as well as the chord structure of songs), the lifelike reproduction of singers and their vocals has to be my personal number one in the reproduction of recorded music.
J. Gordon Holt was a stickler for the reproduction of vocals without what he called "vowel colorations" (he single-handedly created much of the audiophile vocabulary, though Harry Pearson loved to take credit for that accomplishment) . When I read a review of a loudspeaker by JGH in the very first copy of Stereophile I received in 1972, I immediately knew what he was talking about when he used that phrase. We hear voices everyday, and if a loudspeaker (or recording) produces an un-natural tonal-timbral sound, we instantly recognize it as such. How anyone can listen to music through a "colored" loudspeaker is a mystery to me.