I think what makes a performance great goes beyond just technique or interpretation or anything else to which one might easily point. For me, it seems to be an intangible something - something I can't describe well, but have definitely been a part of - a synchronicity that's not just about timing but about togetherness in so much more... it's as if something electric happens and, in my experience, it seems as though everyone present instantly feels this, recognizes it, whether you're playing, or whether you're listening. I can't say what this is, but it's an amazing thing.
THAT's the really good stuff!
JH