I find one characteristic of good lyrics is that they are easier to learn. They are memorable, have clear ideas and original rhymes. I also like good characterisation. I think Dylan has improved at this over the years. Another master of characterisation is Randy Newman. The (probably drunken) macho pig of "You can keep your hat on" is so brilliantly drawn that I don't know how anyone can sing the song with a straight face. More thoughts later. I have a feeling this one will run and run.