Max is an object oriented programming environment, in which the user can program custom midi processing.
Adding MSP allows the user to intergrate audio processing.
Max has been greatly enhanced by the addition of Nato.055. The talented programmer/artist who has created Nato.055 has presented Max users with vast array of visual tools which to work with. If you are interested in learning about nato, you should check out an excellent review of it on bootsquad.com