the only thing hitler was good at was propaganda. the propaganda caused the germans live in an aerian dream, that was thier strength and weakness, you see, morally its great for the people and public support, but thinking you are the chosen one makes you underestimate your enemies. as people said before me, hitler thought all other nations are sub humans and couldnt put up a fight, breaking the iron rule of warfare of "dont underestimate your enemy".
also he made the same mistake of ww1 - germany split its forces into 2, instead of using russia as an ally.though the german army was far better equipped and trained, its command was horrible. hitler was a paranoid, thought anyone are conspiators against him and thus created a complex and tedious chain of command, so only he had complete control of the military. "dont limit your officers in thier authority on the battlefied" sun tzu.
he wasted all aircraft force on a suicidal campaign on britain, used much of the trains to tansport jews rather than ammo, didnt clear up the wounded, and let them die on the field, wasted alot of resoures on the "final solution", and didnt produce cost effective weapon(though 1 panzer could destroy 4 shermans, for every panzer created the allies made 25 shermans).
hitler had the potential of winning, but he crazy as hell(just an example: he wanted to make a great hall in berlin, one so big to house 100,000 poeple... just the body heat of all those people would make the humidity create rain inside the compound, but he didnt gave a damn.)