This is a compile of my opinions about all the stages.
Cell - It was really easy, not much design you can do besides bone size and placement, not 3D design yet. At the begining it depeneds on what mode your playing the game on, on very hard, things own you, on very easy, you own things, eat dead cells, or feast of some growth. Near the end, you can dodge anything, own anything, and it becomes boring.
Creature - Very much design you can do on your creature, placement, how much joints, size of bone, how much bone, how long, how big, it was very entertaining. You get brain size by be-friending, or digesting them, or both. Be-friending wasn't the best, because other people always made their creature the creature with the best singing and dancing to be-friend people in their game, making it hard for you to be-friend their creatures. Destorying them, same thing as be-friending except eating. And the epics seemed to come at random, you kill this and you get a really big boost.
Tribal - You can do lots of things, paint, puting rings, hats and other props on. This stage, also depends on what difficulty you are on, on very easy, I killed an enemy's cheiftan with one person, and half their tribe..on very hard, my people didn't stand a chance.
Civilization - Designing your car and plane, house, factory, fun place, it was all really great! If you are allied with someone, and you remain allies until every other civilization is dead, you win. That's what happened to me, twice. And spice becomes the worlds trade/happiness.
Space - It was a very intruiging, designing my own ship, with the map, the inter-stellar drives, the limit you can travel, the energy, your health, the weapons, the 3-D, the planet fighters, the rays, though the story-line of the grox and the center of the universe.
Evolution - If you come out of the Cell stage an herbivore, then in creature stage, agressive, tribal be-friending, civilization domination, in space, the evolution will give you something cool. If you don't like it, you can change it for like 500,000 spore-bucks.
Over-all, it was a great game, I finished it and all. My favorite stage has to be the creature stage.