His grasp on pacing was horrible - all of his films seemed hurried and rushed through opposed to the previous films. And not at all in a script-based way, but rather the editing and in-scene pacing was pointlessly hurried. It got slightly better when they split Deathly Hallows into two movies, but you could still kind of tell they weren't being paced properly.
All of his films displayed an utter inability to convey dramatic or emotional moments. After the pretty emotionally-charged ending of GOF (a movie that was directed properly), Yates could never recapture anything close to that level of emotionality and dramatism in his films.
All of his movies were extremely...dry. This is probably what you meant by not having a style. Whereas Cuaron interjected a phenomenal amount of whimsical style into his movie, and GOF was consistently emotionally charged - between every scene and every line - Yates' films lacked all of that imbibing of creativity or uniqueness. Instead, between every line in his films there was nothing more than the dry, flat nothingness of a book being put to; screen. I think that's even worse than lacking style, that's the art of making a dead, lifeless film. Which I would say is pretty much the worst thing you could do as a skilled director.