This season is pretty good so far. They have had some stinkers in the later seasons, but so far this one has been golden. I don't have cable so I can't watch the episodes when they air...but
http://www.southparkstudios.com/ is a life saver.
Recent episodes like the KFC Medical Marijuana and Facebook episodes were outstanding. This new one sounds like it's great too.
Matt and Trey have naturally matured past dick and fart jokes, and new material. But they have been even more experimental with testing their audience than Family Guy would ever dare to.
Consider episodes like "Pip" which is Great Expectations retold in 20 min without any other South Park characters, other than "Pip". There are no jokes throughout the entire episode, until the very end where cyborg monkeys came and destroy everything.
Or how about the cliffhanger season finale where you're about to find out who Cartman's father is. First episode of the next season was a Terrance and Phillip mini movie.
The thing is though. This seriously pissed off the show's fans, and the ratings for those episodes were lower than ever.
Episodes like "Simpsons Did It" where Butters is Professor Chaos, and tries to think of the most menacing thing he can do to destroy South Park. The only problem is, everything he thinks of - The Simpsons had already done first. This was influenced by Trey, and Matt comioing up with ideas, and later finding out that The Simpsons had already beat them to it (such as the episode where Bart steals the head off of the Springfield monument).
Consistently writing fresh material within the realms of your imaginary world is hard to do. Especially when said work is as infamous as South Park. For 2 guys to have maintained all of the writing, and most voices (other than Chef, and the females) for 14 years is astounding. Especially when the material pushes controversial censorship boundaries as much as South Park has.
I'm just heavily impressed that it isn't far more stale than it is by now. The political topics certainly do help, but so do the more recent episodes focusing on the adults of the town. But I'm gonna shut up now...