I loved Season 6. It's actually tied with Season 3 as my second favourite season. What most people view as degrading and depressing I view as real, uninhibited, storytelling.
I wouldn't change much about the Spuffy relationship, even the degrading sex. I felt it served a purpose in the show to reflect Buffy's depressed, self-hating psychologically distorted state and it certainly achieved that and then some! If the sex was pointless and just an excuse to show nakedness, then I wouldn't be on board with it.
I would have liked Spike to be a bit more loving towards Buffy though, a slight reflection of his S5 self, but this is really a minor change.
I'd make Dawn have more of a role this season, I like her loneliness arc but the way it was portrayed with her turning into a klepto just felt a bit weak. Similar to what [MENTION=7939]The Ferg[/MENTION] suggested, she could be lonely and do the klepto thing for half the season, then fall into the wrong crowd at school over the course of the second half of the season.
I'd like Xander and Anya to do more in the lead up to "Hell's Bells" because really, they just help Buffy out now and then with Scooby stuff and sit around planning the wedding. Maybe have Anya interact with her vengeance past a bit more. Take it further than just Halfrek. Also, maybe a few scenes with Xander's family pre "Hell's Bells" would be good. Xander could take Anya to meet the family, but then Xander's parents start having a row, getting drunk, being abusive etc. That would be a better lead up to "Hells Bells" because it would make the audience more aware of Xander's reasons for leaving Anya.
Willow's addiction was perfectly executed. Loved it 🙂 And despite loving Willow and Tara together, I think Tara's death and the aftermath to it was brilliant storytelling.
Regarding the Trio, I think they were good, but I think Warren should have branched off on his own sooner so we had more time to see Warren as a misogynistic psychopath than just a silly nerd. Like [MENTION=2271]SMG14Fan[/MENTION] and [MENTION=12230]Mischlings[/MENTION] said, the fact he's just a regular guy, without any innate supernaturalness, makes it all the more interesting.
[MENTION=8404]Blaze[/MENTION], I think if Giles were there then a lot of S6 wouldn't make as much sense. Not to say the Scoobies are children by this stage, but Willow may not have been tempted to go so off the rails, so quickly if Giles were there as somebody else, besides Tara to warn her. Buffy would be far less likely to feel so disconnected from the Scoobies and go boink Spike. Despite the Scoobies drifting apart after high school Buffy and Giles always seemed pretty solid in S5. Giles would have also been there to potentially call off the wedding before "Hell's Bells" happened. Giles did sort of warn/scare Xander about what he was getting into in "All the Way".