I do not condone or agree with anything Hitler has done, but, he was a smart man. Well, in his early years, anyway. He pulled Germany out of the debt it owed AND militarized it over the period of 4 years, against a treaty that was, to be honest, completely unfair to the Germans. Does that justify his actions? Some could argue yes, but most say no.
During the early parts of his rule, Hitler wasn't that bad of a guy, as stated previously, he pulled Germany out of a recession and re-armed it over the period of four years. Before the war even began, yes, he started taking land, but the land he took was historically part of Germany that was taken by the Allies in World War I, which broke the Treaty of Versaille, which was, to be completely honest, a very unfair treaty to the Germans.
Once war broke out in 1939, even Hitler's military tactics were good. Blitzkrieg was a very effective strategy early on in the war (which is where Hitler took most of his land anyway), and managed to sign a peace treaty with the Soviets, allowing them to only have to fight on one front. He managed to capture several countries in only a few months. It was when he decided to turn on the Soviets when everything went wrong for him, but, that is the topic of another discussion.
The holocaust. Always a touchy subject, no matter who you talk to. This one, I can't say Hitler was smart with. He was just racist. That being said, Hitler was not directly in charge of the Holocaust, a man by the name of Heinrich Himmler was. But, I'm not sure if we can place the blame on Himmler; he was a complete nut.
Just to be clear, I do not agree with or support anything Hitler did, and he was, indeed, a very evil man. I'm just saying he was smart, especially at the beginning of his rule. As for the OP, it depends on what you define as "great". But, going into that territory could bring up something else entirely, so, I will refrain. All I'm saying is, while Hitler was evil, he was also smart.