The music references. I have the exact opposite musical tastes that Jeph does, but I thought it was neat that he was letting his obsession leak into the strip- it kind of helped it feel "real". They haven't mentioned music in FOREVER in the strip, and it used to be the one thing they ALL seemed to have in common. A huge chunk of early stuff was "she's a hot Indie Girl" and "OH MY GOD, every Indie Girl in town now has one of those skirts!"
I kind of feel nostalgic for the strips where it was just Faye, Dora & Marten sitting around in an empty coffee shop, shooting the shit and being sassy with each other. It wouldn't be the same if tried now (they know each other too well, and their relationships have all changed), but it'd be cool to see it with other characters. That particular brand of "how young people roll" is fairly true-to-life.
Raven. Oh god, Raven. She was such fun. A bit on the nose as "the Moron of the group", but it was still entertaining, and she was a nice character to bounce off the others- you occasionally need someone who's less-savvy. She had a great design, too.
The club where everyone dressed fancy. That was fun. Seems like Jeph got over that obsession really quick.
Back in the "old days", the characters seemed to act more "young" and were less-exaggerated at times. They said things like "hee hee!", acted cute, and were very immature. Nowadays the more "out there" characters are usually a bit nutty (Hannelore, Emily, etc.), rather than immature. I feel like the cast has "aged up" with the writer without actually having aged-up in the strip, as Jeph used to write them like his cultural baseline, and STILL does, without modifying that for "how young people usually act". Thankfully, their poor decision-making skills is still very much intact.