Oh man!

Every time it evolved to a new level I found myself going "WOW!"

I really loved the Death Star action. Hehehe... I thought he would just put a vulcano in the city, but that was even better.

This is truly revolutionary. I mean listening for other races? Simple yet really cool.
Giving your tribe some things, a drum and then they dance with their little spears around the campfire. And the editor of the creatures... MAN! I can go on. Every aspect of the game was just highly intereting, ok perhaps not the bacteria stage but still it had it's lure with the editor.