Now, i've played ALL the sims games, but none of them sucked me in like this one.
The 1st stage involves you running around finding food and trying not to be eaten by bigger life forms and trying to grow bigger and eat them, and adding defences to your life form this is the primordial soup stage (microbiological stage)
The 2nd Stage pulls you out of the water and sticks you on land. again, eat or be eaten, but this time you can completely change your life form.
The 3rd stage plays like an RTS, but simplified. Though not great as the other stages, its pretty fun
The 4th stage is brilliant. again, a bit like an RTS but a bit more complex, and lets you build land, sea, and air defences.
The 5th stage, The space stage, is the best. from black holes to trading routes, planet terraformers, atmosphere changers and bombs that can blow up entire planets, plus this awsomely cool thing at the center of the universe (dont wanna spoil it for you).
The creature creator is INCREDIBLE. you can build any kind of animal, any kind of building, any type of spaceship, car, plane, boat...
In short, one of the best games ever made.