South Park has always been one of my favourite animations, and I agree that the first seasons were extremely juvenile until they started getting into the Token and the hate crime laws, that's where it became a good show into one of my favourites. The fact they weren't afraid to speak there minds about politics, the justice system, etc.
Even the episodes about Mohammed were amazing and kept me hooked. That irony that years ago they had him on screen with no backlash, part of the title screen, with no backlash, and now, hatred. I've always wanted Kyles speech to be uncensored, but even with it, it added to the humor.
I can understand there boredom though. Over a decade of the same characters, the same voices, the same scenery, the same design, it must get boring. If the show went after this series, I'd be sad to see it go, but I wouldn't blame either creators for it. I can't even imagine how it must be to work on the same show for that long.