I actually recently made a topic on my thoughts for this game so I'll keep my post here brief.
It was a lot of fun, and indeed "fans of the show will like it".
Combat gets a bit repetitive and yeah, putting up status effects on your enemies is both incredibly easy and incredibly effective. Most combat can be over in just one or two turns when you've got someone bleeding, on fire, and grossed out (basically poisoned). Literally each tick of the DoT's can take off half their health. That said, the attacks were pretty fun, as a Fighter I never got tired of the roshambo attack which has you kick the target in the nuts, stunning them for 3 turns.
The story is about what you'd expect from South Park: silly nonsense sprinkled with satire and sarcasm. Stupid plot points that are specifically designed to be stupid for the sake of satire. And as with most episodes of South Park, events escalate rather quickly...day 1 goes by fairly normally, then something happens during the first night that cranks things up a notch in terms of being edgy. Day 2 gets pretty crazy, with an even crazier event taking place on the 2nd night. The 3rd (and final) day is when they go right on over the top with the abortion clinic and...well, lets just say you get to know Mr. Slave a lot better than you probably ever wanted to.
In Conclusion: I'd say unless you're a mega South Park fan, this one can sit comfortably in the "Rental Worthy" category.
Replay Value is, unfortunately, rather low unless you're a huge fan of the series and think that you'd be interested in just playing the game every now and then as though it were one of your favorite episodes that you enjoy watching every now and then. Unless your an achievement whore, there's no real reason to warrant a 2nd or 3rd playthrough. All the items/equipment are always in the same places for every playthrough so once you've played through it once you'll know where to go to get all your favorite gear.
As for the partners, Butters is by far the most useful/effective...and he's the first one that becomes available in the game. The rest aren't bad, really, they're just not as good as Butters.
In Conclusion: Unless you're a huge South Park fan, I'd say this game fits comfortably into the "Rental Worthy" category.