A repost of my response to Brian's latest challenge, on pets:
I'm very interested to see how the dog in Fable 2 plays out. It's a combination of both combat and show, and has uses well beyond those... such as pointing out hidden treasures and reacting to NPCs.
What I loved most about the Creature Handler system in Star Wars: Galaxies was the variety in pet types and ways of acquiring them. By making wild creatures open to taming, the designers provided a huge assortment of potential pets without having to design a lot of pet-only creatures (the wild creatures could be fought and skinned, thereby providing PvE content).
A pet is much more meaningful when it clearly represents a personal choice, individualizing the player. In real life, people show off the individuality of their pets, not the common features. They might describe their pets from afar as "a black lab" or "a beagle", but they always point out the pet's individual personality and appearance when we actually meet it. And the individual characteristics are what we take the most joy in, even when watching wild animals.
Fable 2 allows individual players to train their dogs differently. That's a good example of making pets both personal and meaningful.