What makes a good performance?

Confidence, passion, physical bond with the instrument, creativity (unique style), technical skill, focus, vulnerability, connection with the audience.
Tori Kelly - Dear No One (cover by Leroy Sanchez)
https://www.youtube.com/watch?v=tuq8mktbO54

I think even though this song wasn't wrote by Leroy Sanchez, I really feel his confidence on the belt-y notes, and his vulnerability when he sings higher and looks completely engrossed in the song. His technical skill is also good, as heard in his vocal control when switching from note to note. He also looks very much like he is playing his guitar, rather than vice versa.