2-4 Doctors? Man I can't think of a William Hartnell story that didn't bring a smile to my face. The Aztecs and The Meddling Monk are among my all time favorites.
I've only seen a couple of his stories and thought they were OK but not outstanding though with a few more stories I could perhaps get to like him a bit more and it'd be intresting to see a future incarnation with a similar kind of persona.
As for the others,
5th - Mediocre.
6th - Memorable only for his costume.
7th - Continued the decline in quality.
8th - Can't really comment on him.