The DO is basically an inhuman chaotic and corrupting force, contrary to the order and creation the Creator stands for. The DO wants to break his prison of course. Furthermore, I think he wants/has to destroy all of creation, because it's basically his nature. Possibly he ultimately wants to destroy the Creator as well (maybe, though, there is a cosmic rule, that they can't directly kill each other, a'la Lost). What would happen or what the DO would do if everything else is destroyed is hard to say. Maybe the DO would extinguish as well, or just rest for all eternity. As RJ said, one can't really grasp his motivation with a human mind, because the DO is basically a God.