No shops, no litter, and the zoo is not to big. A little bit music on the background and playing on my own computer. Challenge mode, without food and drink shops. Best way to play this. Don't worry about the animal genes, you can breed your own. No 10K animals in the market, and when you see something you want to buy, no hurry with the mouse clicking. Life is easy, and my animals have a great life. They are not considered retards in challenge mode. 
