There're couple of upside.
1. True to the source with graphic, animation, sound & jokes exactly like the TV show.
2. The whole South Park map to explore with fast travel point perfectly located.
3. Past reference of the TV show.
4. Check point is convieniently placed in case if you're defeated in a battle, you don't have to start over from the beginning of the story arc. You get to save anywhere too.
5. Awesome character customisation.

There're couple of downside.
1. Gameplay mechanics is simple. Too simple for some.
2. Low level cap. You'll max out in the middle of the story.
3. Frame rate drop at certain area of the map. Hopefully they patch this soon.
4. There're aren't any distinction between classes apart from skills. No class specific items.
5. If you get a copy which isn't US region, certain questionable scene will be censored with either get a facepalm statue for EU or crying koala for Australian. PS store Malaysia get the facepalm statue.
6. Some notable characters of South Park are absent.
Does it has replayability value? It depends.

The whole game is like watching an entire season of South Park, which is awesome. However, the simplistic gameplay mechanic may turn you off if you expecting some complexity of an RPG game.