Hard to name just one thing. I am late to the party and only got into BTVS this past year. So I have not come close to see everything there is to see. When I start new shows, I tend to skip around. lol
I LOVE the first 3 seasons. But after that, there's a lot of changes I didn't care for from what I am seeing of them..
1. Tara. Don't dislike her. But from the little i've seen, she doesn't interest me and I preferred Oz.
2. Dawn, also doesn't seem like an appealing character
3. I hated Angel leaving
4. I didn't like that Joyce got killed off
5. I didn't care for Spike becoming a regular cast member, and turning into a Buffy fanboy & stalker.
6. And I hate Spuffy with the fire of 10 suns. I think that pairing was the downfall and destruction of both their characters.
7. I hated how heartless and holier-than-thou Buffy was in season 7, in addition to her automatically always siding with Spike and even kicking her father figure to the curb in favor of him, after everything he's done for her.
8. How everyone ganged up on Buffy after she came home from running away. And they harass her to the point she's in tears, and only think about how her leaving effects them, and not how lost & upset she had to have been to leave. Then they all snub her and act very passive aggressive when she is back, then have the nerve to get pissed off when she decides to try and leave again.Xander was the aboslute worst one in this scenario, followed by Joyce.
9. Again, Xander could show his absolute worst & most petty side when it came to Angel. Especially his lying to Buffy about what Willow said, and her having to kill him because she wasn't kept in the loop about his soul returning. Then after she runs away, Xander says she hopped a bus over boy trouble, when killing her boyfriend & sending him to Hell is FAR from juat boy trouble. His behavior in Revelations was especially sickening. By blabbing about Angel to Faith, he caused the rift with her & Faith. Never-mind he's dating Cordy, and cheating on her with Willow, but has time to judge Buffy over helping Angel, who hasn't caused any harm since he's been back since they didn't even know about him. Honestly, I think Xander eeded to get the snot beaten out of him on occasion. He was NOT the best friend to Buffy, especially when it's out of jealousy because she won't date him.
Hmmmm. The first 6 don't make me sound great. But sadly, the show just goes downhill for me once season 3 ended. If I have to pick an absolute worst out of this list, it has to be 6. Spuffy. Followed by Xander.