A zoos reputation is very easy to hit 4/5 stars. I'd love to have to build a large zoo to hit 5 stars. 5 stars in zoo conservation can be achieved just by releasing exhibit animals, which happens a lot, especially after you added the nice exhibit managment tools. The animal rating needs very few species to hit 5 stars. I enjoy the small milestones whilst building up a zoo, and to look down and have a 4 star zoo with just a few exhibits/habitats, impacts my desire to keep playing. The zoopedia has the conservation status of animals listed, this could be used as weighting for animals release impact on zoo conservation. I know this is a small part of the game, but it strangely has a big impact on my motivations to play. I think it might be down to ZT2 using the star rating to unlock new animals etc for your zoo.