You are a part of the environment.
You are one of several people to play in the game. You will be playing directly with everyone else. There are not three or six options for your race, and there are not only so many options for equippable items or skills you can have. You will be one of hundreds of thousands of playable species, and each species will have hundreds of thousands of possble looks, items, skills, and abilities. Really, items will apply to everyone in a different way, depending on hundreds of different factors.
Players may not always be distinguishable from the environment. You may be a fly on a cave wall, and another player could be an ogre who lives in the cave. You will be buzzing around if you are a fly, unless you are a very talented fly. Based on how many game points you have, which are collected by playing, you may be allowed to speak. If everyone is an animal, suppose there are wolves and wild dogs, and your pack needs to find food in wolf territory, you will probably have a PvP battle extreme, if you get into one at all. Of course, NPCs will be needed at the early stages, especially for simple creatures that nobody wants to play, such as flies or worms.
The environment is definantly out to get you. There are diseases that make you sick, poisonous plants that you accidentally walk through which make you itch, and you could get a sunburn if you stay out in the sun too long. Perhaps you stay underwater too long and drown, or maybe you get chilly and catch a cold, or you may even eat spoiled food and barf it all up.