Gabrielleabelle argued that the Buffy/Angel relationship subverts itself. This is what I picked up on - on a less articulate level - the first time I watched Buffy. I was disappointed when Angel got his soul back and seemed immediately and magically transformed into his good self (when he gets back his soul in Becoming 2, he doesn't remember his soulless period). It shoved the subversion back in the box.
Anyway, so I definitely agree with Gabrielleabelle on that, and recommend her post if you managed to miss it through all these years. But what I was really thinking about was Buffy/Spike. Several months before her Buffy/Angel post, she posted her readers on the question as to whether or not Buffy/Spike was subversive. People had plenty of different ideas on the subject. Here's mine: I think Buffy/Spike follows a subversive pattern that is similar to Buffy/Angel: The relationship is set up in S5/S1, subverted in S2/S6, and the subversion goes back into the box in S3/S7.
Villain falls in love with good guy and decides to redeem themselves is a huge cliché. Bad boy who redeems himself for a good woman is a particular subtype of these cliché that is also very common. Some commentators on Gabriellebelle's post indicated they thought the fact that Buffy does not love him back contradicts the cliché...I'm not so sure. While the revelation of Snape's motivations in the Harry Potter series didn't happen until after Buffy was off the air, it was still around the same time. Snape very much does not get his love - and like Spike, he dies in the end (and actually stays dead). And while Buffy's love does not redeem Spike, he does "earn" her love in the end.
S5 follows the cliché. Despite some initial creepiness on Spike's part, he starts doing genuine good, and earns Buffy's respect (and a kiss). But in S6, things go in an unexpected direction. I've complained in the past about the statement that S6 "ruined" Buffy/Spike. It disturbs me that fans are willing to overlook the violence and creepiness of the earlier parts of their relationship, while seeing a season that shoved these factors in viewer's face as ruining the relationship. Something similar could be said about Buffy/Angel. S1 and early S2 had plenty of creep factor to the relationship. When Angel lost his soul, that brought the horror to the foreground. However, the ostensible divide between souled and soulless Angel meant that fans who didn't want to see the darkness could claim Angel wasn't Angelus, and thus there is no blaming S2 for "ruining" Buffy/Angel.
So, what is the subversion in S6? S6 is too complicated to be a straight and obvious subversion, but one thing is definitely worth noting: the bad-man-redeemed-for-the-love-of-a-good-w
And just as in S2, the season ends with the vampire getting his soul back, and the story line reverts to a straight portrayal of the cliché. (Though for some reason it doesn't bother me this time - less of a divide between souled and soulless Spike, perhaps.)
* The whole "Buffy came back wrong" red herring could itself be seen as a commentary on soulless Angel in S2. Angel did bad shit - but it's not Angel so it doesn't fully count. Buffy thinks that her come-back-wrongness is the explanation for her affair with soulless Spike. Turns out, not so much.