Don't worry twesterm, it gets more complex with each stage. Cell is just point and click, you can't even attack directly. Creature stage has a more RPG feel to it with a variety of attacks, building your stats, and eventually you get to recruit a pack.
The tribal phase gets a little more complex with an RTS building huts for purposes of war, food gathering, or befriending, then the civilization stage ups the complexity again with city management, choosing religious, military or economic city states, then building up the cities by adding houses, factories, entertainment areas, turrets ect, creating all of your own vehicles, and buildings, and trying to take over the world.
The final stage, the space stage is incredible huge and deep and is the meat of the game. I've been in the space stage for about two hours and I've barely scratched the surface, it's freakin amazing. I can't even describe everything you have at your disposal by the time you get to the space stage. You have to terraform planets, build a galactic empire, wage war, make friends, establish trade with other empires, form treaties and alliances, upgrade your custom built ship, build cities, create planets, it's VAST. I can look at the screen and it's filled with more stars than I can count, each star is a solar system, and each solar system has a number of planets. Just going solar system to solar system and exploring planets is incredible.
In an interview I posted he said he (Will Wright) made the game with a gradual curve in complexity and also the order in which videogames developed. Starting with a pacman-esqu simple gobble game, and going through basic action game, RTS, civ style games, until it reaches it's climax of enormous community generated game where the players ultimately have all the control. It's an amazing work of videogame art, and it really is a ton of fun if you're willing to invest the time in it. Wasn't the first 5 or 6 hours of GTA IV just a tutorial?
http://www.vgchartz.com/forum/thread.php?id=41290&start=0
there is the interview with him I posted. Brilliant designer.