Hitler? Absolutely not. He was not a good leader, good commander, or even a seriously important figure in the long run of things.
Really? Come on... that's just crazy talk. Hitler was evil, but he made an impact...
Leadership (for his country)
1) Led Germany from the worst country economically in Europe to the richest (people in Germany were burning money because it was cheaper than fire wood)...
2) Created first "highway" system, that is now used all over the world in countries that can afford it, and is key infrastructure
3) Led his country to numerous (military mainly) technological advances, including rockets
4) Annexed his neighbor Austria
5) Took back the Rhineland (sovereignty of his nation)
6) Annexed Sudetenland and Czeckoslovakia
7) Made Hungary, Romania, and Bulgaria his lackies
Commander
1) Conquered Poland in 2 weeks
2) Conquered France, which the biggest land army in Europe at the time, in 6 weeks
3) Conquered Netherlands, Belgium, Luxembourg, Norway and Denmark with barely any conflict
4) Rolled through "Yugoslavia", don't know the time frame exactly
5) Same with Greece
6) Destroyed over 200 Russian military divisions in the first 2 years
Impact in History
1) Due to Holocaust, Zionist movement took over Israel, which many today attribute at least partially to problems with the Muslim World to this day
2) It took almost the entire civilized world at the time united to defeat his army, and the results left the CCCP in charge of E. Europe, which only recently was made free. Without Hitler being such an a-hole, Russia would never have been able to take over E. Europe like that
3) Today is the epitome of evil, guiding civilized nations in clear terms of how NOT to behave...
I would say his impact overall is pretty much, while clearly a terrible stain in history, an undeniable fact.