It's genuinely laugh-out-loud funny
As satisfying as South Park's combat system is - it's Paper Mario's approach if you want more of an idea - it was never meant to be the main attraction for the game. Much like the television show, though, The Stick Of Truth is genuinely hilarious. It does often lean heavily on 'in-jokes' - Al Gore hiding behind a bush ranting and raving about ManBearPig, for example - but for the most part it's as immediately funny as its TV counterpart. It pulls no punches either, so if something can be made fun of, it will be.
It doesn't water down the humour
My most recent playthrough of South Park focused on the start of the game, from opening cutscene onwards. During this time there were jokes about farts, David Hasselhoff, video games, films, TV, sex, the homeless, the Japanese, and masterbating. It will offend the people who have always been horrified by the series, and will no doubt cause a hooha because now it's happening within a different medium. But it firmly sticks to the Parker/Stone maxim that everything is funny, or nothing is.
Fans will feel catered for
The Stick Of Truth has been designed to throw references at people almost constantly. We've already mentioned ManBearBig, and the dedication to give back to those who have been with the show since day one is of credit to Matt and Trey. That's not to say it's a requirement to have seen every episode - you just have to get the South Park sense of humour - but it's definitely an extra bonus to take away from it.
You get to explore South Park
It's ff absolutely no concern to anyone who's not a fanatic, but there is something incredibly compelling about walking around the environment and seeing how everything is laid out. I unashamedly proclaimed 'So that's where City Wok is!' when I saw its location. Does it make any difference to the game itself? Not at all, but it's an avenue never really explored outside of The Stick Of Truth.
You can be a part of it all
The combat may take a backseat, but that doesn't mean it's bad. In fact, the simplicity of it - which mimics how the TV show has always approached matters - is nothing but a good thing. It's a very stripped back real-time system that caters for the jokes the game wants to tell while still allowing you to be engaged with what you're doing.
The opening of the game is excellent
How many games actually make you laugh? I imagine you can count them on one hand. Here, Trey Parker and Matt Stone have brought their comedic talents across near perfectly. No line is out of place, no character feels watered down, and the situations you find yourselves in manage to straddle a very enjoyable line between making you laugh and gasp in shock at the same time. In short, it's South Park.