What about the game itself? As I went through the first stage (Cell) I was delighted. Even though the graphics were cartoonish and cutesy it was all still quite strange and organic feeling, and the contrast in scale of bigger vs small creatures was really very effective, at times I felt almost awed.
Having played through that stage I thought about Flow (cell stage is like Flow, but with more advanced and colourful graphics), and how that earlier game was really the better one. I set the difficulty to hard and still managed to get through the stage quite easily, even as a herbivore (next time around I'll play as a meat-eater and see if the gameplay changes much). The gameplay in Flow is really great- as you have to line up your attacks on other creatures carefully and go in at the right time- there's a wonderful cat and mouse game going on between hunter vs hunted, and the tables can turn very easily. In Spore, there wasn't really enough of this kind of tension in the gameplay (as a herbavore anyway, maybe I'm being a little unfair here?), you kind of just float around and try to avoid the bigger stuff.
I thought it would have been better to evolve a bit more going from the cell stage to land. By the time you reach land you're basically just the little cell creature you were before but with legs stuck on- I felt millions of years of evolutionary history had awkwardly or conveniently been swept under a rug. Also, I was still having a lot of fun blobbing around in cell stage, and it ended fairly abrubtly.
I don't want to write too much a bout the next stage, as I'm only halfway through...