The characters in QC are familiar, reminiscent of my own circle of friends who are young, single, and dealing with the issue of relationships themselves. There's always a tension between platonic friendship and sexual attraction, and because that often leads to awkward situations there's a lot of humour in how the main characters balance respectable restraint with careless flirtation, the fun they have in each others' company and having conversations laced with graphic innuendo.
Much of the humour is wry and dry, but there are the occasional laugh out loud moments as the reader gets blindsided by a bizarre comment or response. The dialogue is witty, clever and sharp; and it's been a page turner for me 'cos it's fun to see how far Marten and Faye will get on with each other as friends and housemates, but never as lovers though it's obvious that they so want to.
Actually, I know how it turns out for them since I discovered QC only recently, but I've been reading QC from the very first strip to understand the circumstances in which they and their supporting characters are in now. I'm taking it in blocks of 50 strips a day so far, and it's still going to take me many more days to catch up with the current content (as of today, QC is at the 1297th strip). NBS will pedantically calculate it to 26.5 days now that she has the relevant data.
It's also interesting to watch an artist develop his art. Jeph Jacques has been drawing this webcomic for nearly five years now and in that time his initial crude line drawings have evolved into more realistic-looking people. Also, he's put in many more characters and created a more complex relationship web, but it's the consistency of his characters that make them believable: their expressions, postures and gestures are apt and emote well with the dialogue.
I don't really know why I find QC so engaging. Perhaps it's because the characters are easy to identify and identify with. They live regular, mundane existences but they get by with a little help from their friends, and that's what gets to me most. There's nothing like having a small, tight circle of good friends to keep one sane in this world.