His control of the tempo of the fight: throwing jabs to play with the rhythm, alongside his evasive footwork, his exits, his balance and ability to exploit open targets, is really a pleasure to watch.
Especially note the commentary at 2 mins 20ish, 4 mins 30ish and 4 mins 50ish.
EDIT: I found out from a fellow student of Sonny's who follows boxing that they won't put this guy's fights on TV because he is 'too boring'. Anyone who watches this and finds it boring clearly needs to be hit in the head a few more times so they can appreciate how good he really is. ;-)