In season 4 I believe that they were already making too much of an effort for a joke/quote/etc.
Sure I would have liked much more, but it is refreshing to see a show stop when there's no more good stuff coming out, instead of getting on the verge of undoing all the good been done.
I firmly believe that South Park, my favourite show which has absolutely educated me and helped me mature as a person in the past, is now counting more bad seasons than good. A shame.
I thought it was time for a new sig!!!! =D