I have played several Hills courses. He seems to do more of a low end to high end mix than the other big names, especially near his Toledo base.
I have also noticed is that he is still trying new things. Here in DFW, his Heritage Ranch course has an Dell/Redan combo green, for example. At the Legacy in southern Michigan, he has an island green, some alternate fairways, (5th is good) a plateau green par 3 (6th) and chocolated drop mound fields (7th) for instance, that you wouldn't have seen in his work a few years ago.
So, he is doing a good job of keeping his designs fresh, rather than mailing in the same old stuff, which is always the "hazard" of becoming a busy, established gca. I don't know if that is him studying the classics, or his talented staff pushing the envelope, or both. If you have only seen a few of his courses, you might not have the clearest picture of his work, especially his newer stuff.
He does have a book "The Works of Art" which I picked up at the Legacy which details some of his work more.