Galen describes Vader as incorparing many different fighting styles

The apprentice knew exactly what to expect. They had dueled many times before. He had learned how to fight at the hands of the man in the black suit—the man whose face had been forever hidden from him. He knew the intimacies of his refined version of Djem So, a fighting style that incorporated elements of Ataru, Soresu, and Makashi. He had fended off many wild, slashing attacks that would have overwhelmed even an extraordinary Jedi Knight. He had borne the brunt of many psychological battles.

He thought he was ready—and so the sheer severity of the opening blow took him by surprise.

The Force Unleashed I, Chapter 38, Page 436