it was a slick production, with a fully formed flashy website to match, as opposed to being another series hosted on some aggregate site.
it was a production that built on itself through multiple formats, not just a basic "episode 1, episode 2, etc." There were different formats for the cartoons to be in besides just homestar episodes and strong bad emails, and all of them built up on the same set of recurring gags and themes.
As well as cartoons, there were fun games and songs and stuff to click on, and they hid tiny clickable easter eggs in every homepage, menu and in most cartoons.
It was authentically amateurish, and athough it had the general feel of a kids storybook turned into a crude humor comedy, and never relied on either the pop culture references or the 'edgy atitude' to carry the humor of the show in the same way adult-oriented cartoons in the 2000's would. Most of the humor came from randomness, ridiculous situations/interactions, and saying funny words in funny voices, and that concept had not yet been done to death back then.
The relatability to an audience of young computer-using viewers was another huge sign of authenticity. They were riffing on technology topics and websites and webcomics that most everyone active online was using, making spoofs of the video game/action movie tropes that existed in those days, and all the characters in the show - despite having cartoonish identities and roles, largely hung around in dirt lots or back yards, made weapons out of cardboard tubes and duct tape, shot home movies with each other using portable VHS cameras, ding dong ditched their neighbors, bothered the weird guy who ran the corner store, etc. etc. etc.
The characters mostly spent their time in the same way that bored kids who live in the middle of nowhere do, and this might be a big leap, but I think it fills a similar niche as Calvin & Hobbes, which also exemplified the experience of growing up in a tiny town in the midwest
