It is called Dungeon Keepers. Basically you play as the evil overlord and take on the humans inhabiting the continent, as well as other Keepers. The style is pretty much free-form, provided you stick to the rules that there are (which aren't that restricting, only a base template for a generic Keeper). I'm one of the major contributors for both the current one and the previous one.
If you want to check it out for yourself, click here ---> http://forum.spore.com/jforum/posts/list/71011.page