Uhm, let me see. You start your character, you pick a race, a class and a faction. When you're in the game you can pick a specialization, which gives you different talents and additionally you can pick 6 out of 18 extra talents. You can also pick glyphs to change your spells and give you new spells. You can pick professions. You can earn titles, you can unlock over 150 different mounts and a multitude of non-combat pets. You can get lots of different tabards. Your guild can customize their own tabard. You can reforge your gear, you can enchant it, you can put gems in it, you can use item upgrades. And you can completely customize your gear through transmogrification.