Dwight Howard was literally the main reason the Lakers were able to play Kobe Bryant last year. I don't think people realize how damn bad the Lakers defense was and the impact Dwight made on that end.
Howard's problem was that he was injured, he had no real chemistry with anyone on the Lakers, and he had to exert an absurd amount of effort to cover up his teams defensive flaws.
That being said, his lack of lower leg strength and lack of versatility mean that he's a type of player that either had to be built around very specifically or understand he's not a first option offensive player. He's definitely a star and his defensive impact is astronomical though.