Except for 1897 and the atmospheric, ominous, and delightful jaunt into 1995, I don't care for most of the latter story lines. Leviathans, parallel time 1970, and 1840 are only so-so in my opinion--they have equally good and negative things about them but there's nothing in particular that captures my attention or excites me the way that 1795, Quentin's ghost, or the first phoenix storyline and Barnabas's arrival do. And, I absolutely despise the Summer of 1970; I can't even stand to watch that sequence again because I think the writing is so terrible. There was less focus on the original characters in the last two years. The pacing was frenetic--new characters entered the scene (e.g. Hallie, Sebastian, the Todds, Bruno, etc.) and were soon killed off or departed without explanation (Chris, Sabrina, Amy, and Ned) and the plots were convoluted. Many plot features were recycled: although parallel time and the Leviathans were novelties, [spoiler]we twice dealt with possessed children, (David by Quentin and then by Gerard) disembodied limbs, (in 1897 and 1840) and a female character who survives by draining others' warmth (Laura and Angelique).[/spoiler]
I don't know if it's possible to say that there was a "best" or a "worst" year on DS. I tend to care for individual storylines, not necessarily for a year's span of shows, and I've noticed that the show tends to follow a pattern of brilliant stories (1795, 1897, 1995) that alternate with stories I don't really like (Adam & Eve, Leviathans, Gerard & Daphne) within the same year. However, I agree that 1969-1970 was certainly the show's most ambitious year; I think that was mainly due to the pressures that DC put on the writers to maintain a fast-paced show full of cliffhangers to keep the kids tuning in.
ProfStokes