Many people are making the mistake of assuming brilliance to be a positive trait. It is not. It is a neutral trait. It's what you do with the neutral traits you possess that makes you an overall positive or negative influence in the world. Brilliance and evil are NOT mutually exclusive.
That said, was Hitler a brilliant man?
Not particularly. He was good at a few things, such as public speaking, and enough people found him charismatic enough to follow him and put him in the position to take advantage of the times, mainly the Great Depression, that made his words connect with people when just a few years earlier, when times were good, very few were listening. Even during the Weimar days of hyperinflation, which Germany recovered from prior to the early 1930s, few were listening.
I would say that Goebbels was a brilliant man before I would say Hitler was. Propaganda was what primarily put the Nazis in power, and Goebbels was a brilliant propagandist.