It's kind of hard to take the main antagonist away from a movie, and judge it. You may as well ask "Besides Hannibal Lector, why do you love 'Silence of the Lambs'?"
It was well made, I guess? Acting was strong. Cinematography was on point. What do you want? Would it work without The Joker? Probably not. Nor would "Star Wars" work without Darth Vader.