Very different styles, Pat, Dallas and some others already said most, only thing I'd add is Foreman was just a very heavy handed guy in general, all his punches hurt, he got a clubbing like power, Wilder's bread and butter is his explosive straight or overhand right, he has to throw it fast and snappy in order to do damage and his other kind of punches are not as powerful, he isn't heavy handed, more like athletic with one great punch that he learned to set up very well (against lesser opponents) to his credit.
And Foreman didn't panick when he was pressed by someone the way Wilder does, Wilder's game falls apart once someone is getting too close to him, Foreman had his tools to fight in a phone booth when he had to and he routinely beat up great pressure fighters like Frazier or Norton