The basic premise of the game is "eat or be eaten." As you maneuver your character through 18 different levels of gameplay, all of which increase in difficulty, you will need to find power ups, defense mechanisms and any other available "bonuses" in order to create a stronger creature than those you fight against.
As previously mentioned, your character isn't stuck in "device play" and can in fact play online against friends and other random players. This is a great option if you want to build up your character while proving that you're the best player on Spore. At the same time, the gameplay is actually very fast. On the T-Mobile Edge network, we didn't experience any slow gameplay and the game even completed the initial network connection in a matter of seconds.
Here are a few ways you can change the way your character acts: increasing offense, defense, perception, and movement. The game is very perceptive to exactly how much of each category your character has and those areas will determine how well you fight (damage you give) and defend yourself (equivalent of hitpoints on RPGs).
Gameplay is easy to pick up after reading through various directions and you'll find the actual game loads quickly and plays just as fast.