The microwave changes the texture of the food.
Secondly, the microwave literally breaks apart the cellular structure and it changes the molecular structure of your food.
It also through the destruction of cellular structure creates a harmful radiolytic compound.
It also has been proven in studies to change your blood chemistry, increasing your cholesterol levels rapidly, decreasing your hemoglobin and lymphocytes.
Microwaves also leak which can hurt you the consumer.
Helpful Links:
The Proven Dangers of Microwaves
Do Microwave Ovens Pose Health Risks?