GameSpy has an excellent 5 page review of Spore.
As the creature phase started, the game started to give us specific goals to achieve. “Eat a fruit,” the game instructed us. We explored the area around our nest (noting that a baby version of our creature was following us around) and found a strange cactus-like plant burdened with ripe, red fruit. We clicked away and devoured a snack. Mission accomplished.
Other goals that soon appeared included “find a new part” (you’re still on the prowl for new genetic material) and “make a friend” (which encouraged us to interact with other creatures.) Every creature in the game has different ways you can earn its trust. Those with ears might enjoy it if you sing to them. Others might enjoy dancing. These options became available as we discovered the many strange creatures ambling around the map with us. Making friends with other species provides different benefits, like help defending your nest or the chance to use their nests to heal yourself.