So I've read almost all the stories in Threadbare SP
and I have to say that this is a really good series! :) And here's why! Charlie is a really well rounded character, and I think her best feature is being a good female character. Not every female character has to be written like her, but she gives us a break from the usual mold. She's not girlie and gossipy like the other South Park girls, making her standout. Another interesting thing is that she's a female character that isn't built up by her gender. What this means is that she's thought of with traits first, and gender second. And its a refreshing change to have a character be thought around their personality instead of their gender- an easy trap for anyone with their characters. Professional and non.
Now, moving away from the central focus, on to the content. It does feel like the original show! And what's a bonus for me is that it feels like the show in the first few seasons- my favorite! Cartman is still a jerk, but he's a jerk with a /heart/- not some sadistic sociopath. I can relate to him and understand why he is the way he is. Beyond that, the pacing is nice, the dialog is accurate and hilarious and the plot ideas are interesting. Charlie's backstory in the trilogy will give readers suspense and even episodes after that are just as good. Especially the Valentines Day one. You'll know what I mean when you read it.
All in all, if you want to see a fresh, original character in the South Park world that isn't the center of the universe, come and read these series of fanfictions! While the Author is on some sort of hiatus as far as I know, what you can archive is worth it!