As with the South Park FPS game, this is a me-too entry into a popular genre that executes at a kinda OK level but is nowhere near the sophistication and polish of category leaders like Diddy Kong and Mario Kart. A frustrating "drive over the really small checkpoints in order" system and poor balancing of the computer racers also makes it more anarchic for multiplayer but a real pain in the butt to play solo, especially when being forced to run into or shoot other players comes into the mix.
As with the FPS game, the one big strength here is in capturing the art style and vibe of the early years of the show. There's a pretty impressive roster of characters (though you have to unlock most of them) that have an equally impressive array of situation-appropriate voice clips.
That's about where you'll finish being impressed, though. The actual racing action is a subpar copy of the better N64 racers with sloppier play control, obnoxious computer AI and a worse single-player structure. At least with the FPS game, you could pretty much ignore the single-player campaign, or just bust through it with ease if there was something in there you wanted to unlock. South Park Rally railroads you into it as you can't use any tracks in multiplayer mode besides the very first one until you place first in single-player.
You absolutely have to place first to move on, which is a tall task in most levels thanks to the sloppy play control and some awful rubberbanding AI that picks one guy out to sprint way ahead of the pack, and then if you manage to get ahead of them they'll be magically right back up your ass in a few seconds. After the first race, most races also stop being about straight racing and instead force you into a multiplayer battle mode with a bunch of computer AI. These usually involve bumping into someone and picking something up to hold while you cross checkpoints, which is pretty tough as the computer does not have to deal with the sloppy control, confusing perspective and looking at the mini-map to navigate to the next checkpoint like a human player does.
In the end this one just isn't worth the trouble. It's not completely horrid, but the dev team either didn't have the chops or wasn't given the time/budget to execute at the level of the Nintendo and Rare racers on the system.