Am I alone when I say that the level of ratings is not a reasonable measure of the popularity of the storyline? Sure they may be correllated, but many other things affect the ratings. The best story ever could have been the very first one, but not as many people had heard of the show yet, so it didn't get watched as much.
Also, I suspect the true dark shadows fans watched the whole series, but just had personal opinions about which stories were the best. The fluctuations in the ratings are likely due to transient fans who likely didn't follow whole storylines regularly, and thus do not fully reflect the quality of the storyline