I'm glad I kept watching at the beginning of Season 6 when I was briefly convinced it had jumped the shark. I persisted since I hadn't gotten to the musical episode yet (watching some of the more uninspired episodes at 1.5x with captions on). I would have bet money against things improving after Giles -- my favorite character -- left the show.
I found Seasons 2 and 3 to be the strongest, though I was often frustrated by "filler" episodes that did very little to advance the overall season arc. They seemed to find a better balance of that in some of the later seasons, though obviously I found the earlier arcs more compelling. Season 4 raised danger flags, but turned out ok. In fact, I found the beginnings of the seasons in general to be quite weak.
My dislike for Anya waxed and waned; my feelings for Cordelia were similar (sidenote: "Cordy" is the worst nickname ever).
I don't understand why the fan community in general seems to hate Kennedy. I liked her fine, and she was a huge improvement over Tara, who I hated for every single minute of her screen time.
Willow was hottest between the time that Oz left the series and Tara joined, by the way.
It was fun recognizing many of the Potentials from their later work. I also liked seeing Nathan Fillion for a multi-episode arc.
My favorite characters were Giles, Willow (usually), and Spike. Maybe I like accents? I was indifferent to annoyed by Xander and Dawn. Buffy was best around the middle of the series, she annoyed me a lot at the beginning and the end. I mostly liked Faith, minus "5 by 5". I really liked Oz while he was around.
As far as villains, I liked Angelus and the Mayer the best (perhaps obviously, since I liked seasons 2-3 best). The Master was in my estimation the worst by far.
Overall gripe: Too many "filler" episodes. I know it's hard for me to get by liking House and making this complaint, but House is a far stronger character than Buffy.
Favorite moment: Oz and Cordelia rescue Willow and Xander.
Least favorite moment: Dawn tries out for cheerleading. (Disclaimer: That *is* still pretty fresh in my mind.)
Worst episode: I think there are a lot of contenders for this one. The one that sticks out in my mind is the swim team. The Dawn/Cheerleading episode is at least amusing once the horribly embarrassing try-out part is done. Although, hold on, I'm remembering one with caveman beer whose only redeeming moment was Willow pretending to be an idiot. And the hyena one was pretty bad, though it did allow for the introduction of Principal Snyder.
Oh, and as far as I know, angel_grrl never warmed up to it in the least. Still loathes Buffy and friends with every fiber of her being.