Women's sizes are anatomically correct. Zip it up and take a deep breath. Wear the suit for five minutes or so. Ideally, a wetsuit should touch you everywhere without stretching too much. Fighting to get the suit to stretch wastes energy, and stretched neoprene is thinner.
Neoprene is waterproof.
Water can't penetrate the fabric to your skin. When this thin, neoprene is very stretchy, so it hugs your body without the wrinkles and bags that would pump water in and out whenever you move. Less flow means less heat loss. Water flow over bare skin is usually a diver's biggest source of heat loss in warm water. Neoprene skins dry at least as fast as fleece suits and cost, on average, about half as much as fleece suits.