The main goal of the game is to let players create things, and to allow them to share these creations transparently. You don't need to visit a website to download new content, but instead the game will constantly download things from the server. Similarly, content you create is also constantly uploaded, as long as you're connected to the internet. By getting regular "Multiverse" reports, you'll see how other players reacted when they saw your creature in their game.
The editor, which is the same for creatures, buildings and vehicles, is simple and is like "playing with blocks of clay." You can easily add or remove things, or deform them, all by using the mouse. You can create the oddest things with ease. Something that the final game will also have is a procedural texture creator, that's used to skin the things you create. That feature isn't working yet though.
A stage that's still pretty vague is the one where you have to conquer the planet. You can control everything either culturally, economically, or militarily. The latter is quite obvious, and you can spawn and buy vehicles. The actual amount of control over the combat is still to be determined though.
GameSpy also noticed that every planet looks different. There are plain rocks, pieces of ice, and planets that are livable - but even then they are quite varied. If you don't like one of them, you can simply blow them up. Another nice feature is that, if you want, you can develop a creature entirely underwater. These creatures can, when they colonise another planet, build a dome filled with water around their cities, and so survive there too.
Despite the content being shared, it's no massive multiplayer game, and players can't spoil each others games. You can find the exact details in the preview.