Great gameplay, few bugs, and very replayable.
SPore also creates an interesting experience at each level (Although somewhat easy through the first three stages). By far the space stage is the most interesting stage, but also the hardest. With an extreme amount of planets and possible other races to meet in space (Thanks to the auto content downlaod from Sporepedia.)
The biggest gamebreaking bug is spore is the "Ocean creature" bug... In which you're nest ends up in the middle of the ocean and you are unable to go to land to meet other creatures.
But the overall gameplay, replayability, and innovativeness of Spore give the game an 8.5 from me.