2. Fresh imagery (not cliches)
3. Economy in words
4. Marriage to music
5. A sense of structure (pentameter and song form)
6. Some who have sophisticated harmony and melodic development.
7. Focus (keeping the idea from wandering)
8. Vernacular (natural speech patterns unaffected)
9. Versatility (a sign of mastery of craft)

If you haven't already read it, I recommend Jimmy Webb's wonderful book on songwriting, "Tunesmith".

Frank Hamilton