With all these other elements -- visuals, humor, voice acting -- looking as though they've been nailed, the one big question mark becomes the gameplay itself. Developer Obsidian's track record has its ups and downs; although its games often have great ideas, the execution is not always what it could be. (Alpha Protocol, in particular, serves as a great example of that.) What it's trying to do with Stick of Truth does not appear to be the most complex or innovative thing. Its apparent Super Mario RPG inspiration has been cited more than once; hearkening back to older titles to some degree matches the relatively crude look of South Park. And if aspects of Mario RPG are rearing their head, that makes it possible that Chrono Trigger could also be serving as a source of inspiration. I think I speak for many RPG fans when I say I am more than OK with that.
At the same time, I'm hopeful Obsidian doesn't settle for nothing more than replicating the sort of 16-bit RPG gameplay seen in Mario RPG and its contemporaries and then layering all of this South Park goodness on top of it. Indications are that it draws heavily from such games, which is all well and good, but I want to see something more. I'm happy the combat system entails more player interaction than selecting an attack and waiting for both sides' turns to play out. But as I'm currently playing through Paper Mario: Sticker Star and seeing what kind of truly interesting ideas can be fit within the framework of fairly standard RPG combat, the prospect of going back to something comparatively vanilla doesn't sound especially appealing to me.