Incredible. You will be playing this for hours on end...

User Rating: 9 | Spore Creature Creator PC
Incredible. You will be playing this for hours on end. There are so many things you can do with this game. This is just a teaser for the full thing, but it's worth a measly $10. If you want to try it first, there is a demo on their site, that has 1/4 of everything there is. Graphics are really good, but it won't work well unless you have a newer computer(no more than 2 or 3 years old).
The only cons are the sometimes awkward movements of the creatures, and the limits on total size and complexity. Also the forced Bilateral symmetry gets a little annoying after a while.

I've personally made 25 creatures so far, just going over and editing until they look good, but if you want you could churn out hundreds in a week or so. So it's up to you on the time required to make a creation.
All around great game, worth any penny. Makes you wonder how awesome Spore will be...