Seems alot of people are complaining that we didn't get an actual South Park ep, the T&P ep sucked, and we didn't find out who Cartman's father was.
I, too, was disappointed. I also thought 30 minutes was a little long for the one joke T&P characters, but the show was pretty freakin funny.
But in all the messages I've read, no one mentioned that during the closing credits they mentioned that in the next new episode in May we will finally find out who Cartman's father is.