Too soon: The Critic. We deserved more than 23 episodes of this brilliant show. It's too bad that the first season was on ABC who didn't know what to do with it, as they put it on before Home Improvement which was a completely different concept.
Too late: King of the Hill. It should've ended when Luanne and Lucky got married like it supposed to. Few of the episodes after that were memorable, and the finale wasn't as good as it could've been.
Both: Family Guy. The pre cancellation seasons were funny and the first couple of seasons after the revival were as well, but it insisted upon itself after awhile and the characters became more mean spirited than they originally were.