Firstly the cell stage to the civilization stage is training!! Each of the stages brings in more elements slowly educating you in ecosystems and civilizations (in the game anyway) and preparing you for the main part of the game which is space stage.
The early parts are enjoyable, cell stage for instance is a nice little arcade shooter taking less than 30 min to complete. I also particularly enjoyed the creature stage but it took me less than an hour to complete. A quick note here, you don't have to move to the next stage as soon as you can, you can wait and continue to play.
The space stage is gigantic and supprisingly hard (at least for me cos i wanted to play a peaceful race). Once you get into terraforming planets and setting up ecosystems it becomes really fun. My favourite past time is finding barren worlds rich in resources and turning them into perfect paradises. Also sucking the atmosphere off the planet of a race you don't like can be good too.
There are already some fantastic creations in the game available for download and just sitting outside the main game and making buildings or spaceships or creatures can be addictive.
Overall spore is a very good game that anyone can enjoy, i didn't like the sims but i do like this. Very good game for anyone and should get kids thinking about science which is always a bonus.