Unlike Lisa I don't work for the company but I love this game. I've been playing Creatures for 10 years now, starting way back with Creatures 1 and I have to say this is the best game yet.
A lot of people get put off Creatures because it won't hold you hand and walk you through it - theres no pre-defined goals or levels. But the beauty of it is that you're then free to make up your own. You can play with individual norns (or grendels or ettins) breed them to make cool new versions, even make your own add-ons, and of course explore the thousands of add-ons made by other people.
Combine that with the fact that the game will never, ever run the same way twice and theres just so much scope that I couldn't ever imagine getting bored with this game. And really, what more do you need?
Oh and they also have excellent support, both from the company (in the form of my fellow reviewer Lisa) and from the fans themselves, who are always ready and willing to help you out with any problems.