I'm a rabid South Park fan so maybe I'm crazy but this game seems like the real fucking deal and I want to "vote with my wallet" and show that I want more games like this. Rent it if you want but don't complain when it sells like shit and we don't get more games like it because a perception that it's not long enough. What the hell does that even mean?
I'm disappointed by the length because:
1) I've never heard of an RPG being this short.
2) I don't like turn-based RPGs, so exploration and side quests are particularly important to me in this case.
3) They've been working on the game for 3-4 years so I was expecting a longer game.
4) Matt and Trey have indicated they don't plan on making another South Park game, so this is likely all we'll get. Therefore, more content would have been great.
That said, I don't see what the big deal is. I said I'm disappointed with the length and performance issues and so I might rent it for now (with a possible purchase later). I'm still going to love the game and enjoy the experience.