As with most expansion packs, Endangered Species breaths fresh life into a title that may have gotten stale on your hard drive. Fans of the original game will enjoy the newly expanded library of animals and objects when updating their zoos.
There are some good additions, but stuff that I would have expected to be added on top of a different major theme. I guess when it comes to zoos, it's a little harder to find new topics for great expansions.
If you spent weeks building the perfect parks, unlocking new content, and wandering around as a guest [in the original], you'll get a little more mileage out of this expansion, but even then, you might find it a little skimpy.