Last couple south park game were pretty good. Decent enough games, but enough south park humour to make them enjoyable for fans. Can't speak to the n64 game though.
As far as i remember the games back then were pretty shit, because they just told random game studios to make South park games. The games were just clones of other games like mario kart. (I did like that dumb ps1 game tho) and trey and matt weren't really happy with it so they "made their own" starting with stick of truth. That's why there was a sudden shift in quality.