I've played through the first four stages of the game so far (cell, creature, tribal and part of civilization), and its a gorgeous, gorgeous game.
Right now it feels like its a quick play-through, however enjoyable it may be. I do wish there was a little bit more depth to the first three stages (I played through the first three stages in about 5 hours), though the fourth stage seems to have a lot of 'layers' so far. I've heard that the Space stage is like playing a whole new game, so I'm really looking forward to that. :)I also hope that in future expansions that the game play is deepened even more! I can see a lot more layers being put into each level of the game, to enrich the experience further.
One of the coolest features of this game is the editor--you can create your monsters, buildings, and vehicles through the editor, and the combination are endless--There are more unique creatures in the 'Sporepedia' than exist in the real world!
It is available for MAC & PC, if you liked the Sims & science fiction, go ahead and give this a shot. :)