It's pretty fun. Lots of good videos on youtube if you search for "spore trailer".

It's the latest game by the creator of the Sims and Sim City.

You start out as like a little amoeba in the water and you have to evolve into a land creature. Then you evolve into a civilization, etc. Eventually you conquer the planet, and then you start conquering other planets.

It's pretty fun, but the real fun is creating creatures. As you eat/kill other ones, you evolve and get new features that make you better. I only played it about 30 min, but it was fun.