Frederick the Great considered Washington's crossing of the Delaware and his campaign that followed in New Jersey one of the most brilliant ever.
Washington had some flaws that keep him from the ranks of the all-time greatest generals (sometimes tried plans too complicated for his inexperienced troops, had problems selecting good subordinate generals, which really handicapped him) but he's among the best of the 18th Century.
I don't think Washington was a great strategerist like a Napoleon or Robert E. Lee but he understood what needed to be done in order to win the war.
Frederick the Great was probably impressed that Washington's battle plan survived the first shot. Victory at Trenton against Britain's Hessian mercenaries was incredible.