Amalgamated Whedon - Dollhouse and previous, better shows
I did my own Buffy marathon re-watch a while ago and here's how I ranked the seasons at the end...
Season 7: It actually started off pretty strongly but started struggling around episode 10. Outside of a couple episodes, the second half largely did nothing for me.
Season 4: Yeah, despite my above post, it's going here. For as great as several of the episodes were, the overall plot was just so underachieved. It only goes above S7 due to the handful of great episodes but it never quite felt like the writers were comfortable with moving on from high school and the sudden loss of characters: Oz, Wesley, Angel, and Cordelia.
Season 1: There's just a certain charm about this season, even if half the episodes are really poor. The second half is surprisingly strong and I wonder how The Master could have fared with the later writing staff.
Season 2: It's basically saved by the Angelus/Spike/Drusilla triangle really. It has a lot of the worst episodes of Buffy ever (Some Assembly Required, Reptile Boy, Bad Eggs, and Go Fish). It goes here in part due to the sheer greatness of the Angelus character as well as several really underrated episodes in "Lie To Me", "Phases", and "Bewitched, Bothered, and Bewildered."
Season 6: If asked a while ago, this would be at the bottom. This season has grown on me a ton and it's largely all thanks to the acting job by Sarah Michelle Gellar. Nuanced and subtle from episode 1 on, it's arguably her best season long job ever. All of the other characters have just enough impact (Xander/Anya, Willow/Tara, Spike/Buffy) even if the magic = drug metaphor was absolutely retarded. This is one of those seasons that's just really solid all the way through even if there's just one real truly standout episode (OMWF although a bit overrated).
Season 5: Maybe the tightest seasonal arc of any Buffy season. Has THREE of the best episodes to ever air in the series (Fool For Love, The Body, and The Gift) and almost every other episode is at the very least, solid. The weakest episodes are probably "Buffy vs. Dracula" or "I Was Made to Love You" but you had the fun mockery of Dracula and the introduction of Warren Mears as a character (and really the start of Spike's crush turning into obsession).
Season 3: Similar to Season 2 plot wise with some weak episodes here and there (I'm looking at you "Beauty and the Beasts") but it is the peak of character writing in my opinion. Introduction of Wesley, Faith, The Mayor, and Anya. Marks the return of Angel and his eventual departure (as well as the departures of Wesley and Cordelia). Spike's return marks the best single episode appearance in the entire series. Vampire Willow appears and is so popular (in an alternate universe episode!) that she gets a SECOND episode in the same season. Every major character has a great standalone episode centered on them and it all just rocks.