Can't really narrow it down I'd find it easier to say why I disliked a musician than why I liked one.
Skill - Knowledge of the basic concepts of the instrument.
Technique - How well the musician physically applies his or her knowledge.
Style - The way the musician plays - what genre he or she plays in and how he or she does it.
Innovation: The musician has a unique form of playing and has developed a new playing style.
Virtuosity - Screw all that, I just want the musician to drop a killer solo! Whooo!
Can't really narrow it down I'd find it easier to say why I disliked a musician than why I liked one.