You have 20 guesses to find the mystery animal of the day. Each fail gives you the most recent common ancestor, so that you can refine the next guess.
Great concept, I am only frustrated by the species selection, which was designed to represent what people are "familiar" with, hence it is really biased for vertebrates, and especially mammals.
Well, Science is one of the most prestigious journal for peer-reviewed scientific articles, so yes, it's good.