Dawn Finally Arrives/Origins of the Slayer
This is probably an unpopular opinion, but I liked the addition of Dawn to the cast. Giving Buffy a sister changed the dynamic of the show in a positive way. In some ways, it could have been seen as desperate, as the show spent all of season four floundering around, looking for a direction. And perhaps that's why this season works for me -- from the first episode, it's about something. There's a level of cohesion across all 22 episodes that we haven't seen since season three, and season five actually does it better.
The cohesion comes from Buffy digging into the origins of the Slayer, something that was hinted at in the season four finale. This show has always worked best when it embraced its mythology, but it often seemed to shy away from that, perhaps as a way to gain new viewers. But staying on the surface is why season four (and season six) were so hard to enjoy. The drama was manufactured, which was all the more frustrating when avenues for organic drama were available.
Dawn was sent to Buffy because she's the Slayer (side bar: technically speaking, she should have been sent to Faith, but I guess the monks did their research before assigning the Key to a protector). It has nothing to do with who Buffy is, it has to do with her lineage. In one, simple move, they've expanded Buffy's role beyond the city limits of Sunnydale. She has a larger part to play in the world, and this season goes along way towards making that clear. High school is over Buffy; it's time to grow-up.
Thanks to a shockingly well written premiere featuring Dracula, Buffy becomes motivated to find out what she is even before Dawn is introduced. And with Buffy's new found enthusiasm for being a Slayer comes new found motivation for Giles, who spent all of last season as something of a hanger-on.
Speaking of hanger-ons, this season actually manages to accomplish the nigh impossible task of making Spike relevant and, better yet, making his continued existence seem less unbearably stupid. Giles can provide Buffy with all the information in the world, but what she needs are details from someone who actually lived it. Spike telling Buffy about the two Slayers he's killed was some of the best stuff of the season.
Granted, that also forces us to ignore the fact that Spike, who has killed two Slayers, should have been dusted by now, but we do what we can.
The Scooby Gang
The introduction of Spike being in love with Buffy actually works initially because it's a response to his inability to kill her. He's obsessed, and since he can no longer express that obsession through violence, it twists into a perverted love. It's nicely done and almost makes up for the last season of Spike, but it's sadly
Willow arguably receives the least screen time of the Scooby Gang, which is fine, as they are able to focus on her relationship with Tara and her dynamic with Xander and Anya more. Willow coming out in season four was enough of a change that just dealing with that over the course of season five was enough. They did a nice job of slowly showing her increasing power, too, without resorting to the stupidity coming next season.
Tara and Anya both get nice spotlights. Both stories are rooted in the characters' pasts and both make good use of their connections within the Scooby Gang. While Tara's episode was more emotional, Anya's ends up working better, if only because it captures the group dynamic better.
Xander finally gets the episode that we've been waiting for since he was introduced. Honestly, Xander peaks in season five, which is great at the time, but unravels in the next season. While he was adrift at seas all of last season, he comes into his own in season five, and suddenly you seem as the most stable member of the group.
Riley is all but largely destroyed in season five. His story makes up much of what went wrong during this season. He could have been an interesting addition to the group, particularly when placed at odds with Xander, but he was entirely defined by Buffy, and he wasn't going to survive like that.
In the End...
Despite all the positives, the cracks definitely begin to show during season five. Perhaps because of the meandering nature of season four, the writers spend a lot of time placing the focus on Buffy even when it's unnatural. Like it or not, but there are times when Giles is more qualified to make decisions than Buffy. It's
Listen, as much as I loved the musical and a handful of episodes from season seven (like the premiere, "Him," and "Conversations with Dead People") it's hard not to feel like Buffy would have been better served by ending with season five. Sure, we'd need an extra episode to wrap things up, bug given how powerful the season five finale is, and how mediocre (at best) the final two seasons were, you have to wonder if they should have gone out on top.
Stand out episodes: The Body (top 5), the Gift (top 5), The Replacement, Fool For Love, Checkpoint