I like almost all of the episodes I've seen -- some of those were groaners, and they pretty obviously wanted us to groan.
They'll make a pun so bad you didn't even think of it. They'll run out every cliche in the book, mock themselves while they do it, and then make an episode about doing it. They'll stretch out the most foul ideas and explore every nook and cranny until they get you to finally laugh. They'll sink to the gutter in .5s when you least expect it. Over the years they've gotten very good at covering up their set-ups, and bits of sleight-of-hand, so it can still be "out of nowhere" even when you know it's coming.
Though it started out as two guys doing silly voices to the construction-paper version of Flash, and is now two guys doing silly voices to the Flash version of construction-paper... it has always oozed craftsmanship and intent. But yes, if you give creative people money and editorial control, they'll eventually just fuck with you for the sake of it, and boy do those two like fucking with people (the first few shots of Team America caused an exec to scream "they fucked us again!")
What I find very interesting, when talking to people who don't like it, or once did and stopped, is that you can sometimes pinpoint when and where they gave up, just from the description of what the show "became" in their eyes. The same is true for people who defend it: you can usually tell what stretch was the peak of their viewing. The show changes, so much, while Matt and Trey's indistinguishable voice (love it or hate it) runs through it all.
That's my favorite bit about it -- rather than slowly shift, or cycle through old bit characters with nothing new to say? Different stretches, seasons, and episodes can operate in completely different modes, and they've established a great toolbox (and quite the sandbox) along the way. They just fuck around with what amuses them, and mercilessly fuck with what displeases them, and this either amuses or displeases you.
At its best, it's given me some of the best (media-related) laughs in my life. At its worst, it's still better than most of the lazy joke dispenaries and pompous bullshit floating around there, as long as you don't expect it to suddenly not be South Park. I was pleased when I heard about those first quest drafts getting rejected -- I don't want to play through a prolonged video game joke. I want South Park, carefully, precisely adorned with each and every bit of mad bullshit they've come up with over the years.