Several things about Homestar Runner that appeal to me:

*Probably above all, the surreal humor. I really don't know how to describe this objectively, but TBC have created a bizarre little world where some characters do the strangest things and others react to the weirdness amusingly, and for the most part made it all seem believable and unforced. That just appeals to me.
*The whole site has a very "experimental" feel to it-since they're not tied down by ratings, sponsors, or even any overarching plot to speak of, TBC aren't afraid to try new things. You get the feeling that they'll never run out of ideas.
*The subtle internal humor. One of my favorite jokes on the site is that square crate you see Homestar standing on sometimes. In case you never noticed, it's labeled with the number of objects it contains. Every time it appears, the number goes up by one from what it was in its last appearance. Every time I see that box, I laugh a little. There's a bunch of similar little internal references scattered around the site, most of which you won't even notice unless you've see another toon.
*Homestar Runner, is, for the most part, truly "for all ages". Contrary to what most mainstream media thinks, that doesn't mean "for kids". In regards to, among other things, the pop culture references, it manages to appeal to kids without feeling dumbed-down and appeal to older viewers without being inappropriate. Not that "inappropriate" material really bothers me, it's just that usually when it's used for humor it falls flat and comes across as really, really dumb.
*The content of the site is free to anyone who already has internet access.
*The cartoons can be watched any time, and the toons are so short I don't have to devote much time to watching them. Even if I have less than an hour of waking free time a day (which has been the case at times) I can still keep up with them.

Hope that helps. I know those last two things might not be quite what you're looking for, but they've certainly contributed to my watching the site for nearly six years.

Several things about Homestar Runner that appeal to me:

*Probably above all, the surreal humor. I really don't know how to describe this objectively, but TBC have created a bizarre little world where some characters do the strangest things and others react to the weirdness amusingly, and for the most part made it all seem believable and unforced. That just appeals to me.
*The whole site has a very "experimental" feel to it-since they're not tied down by ratings, sponsors, or even any overarching plot to speak of, TBC aren't afraid to try new things. You get the feeling that they'll never run out of ideas.
*The subtle internal humor. One of my favorite jokes on the site is that square crate you see Homestar standing on sometimes. In case you never noticed, it's labeled with the number of objects it contains. Every time it appears, the number goes up by one from what it was in its last appearance. Every time I see that box, I laugh a little. There's a bunch of similar little internal references scattered around the site, most of which you won't even notice unless you've see another toon.
*Homestar Runner, is, for the most part, truly "for all ages". Contrary to what most mainstream media thinks, that doesn't mean "for kids". In regards to, among other things, the pop culture references, it manages to appeal to kids without feeling dumbed-down and appeal to older viewers without being inappropriate. Not that "inappropriate" material really bothers me, it's just that usually when it's used for humor it falls flat and comes across as really, really dumb.
*The content of the site is free to anyone who already has internet access.
*The cartoons can be watched any time, and the toons are so short I don't have to devote much time to watching them. Even if I have less than an hour of waking free time a day (which has been the case at times) I can still keep up with them.

Hope that helps. I know those last two things might not be quite what you're looking for, but they've certainly contributed to my watching the site for nearly six years.