I'm not an expert on the matter but from what I understand he nailed it pretty tight at a time when people were telling him he was a loon and needed to shut up. It was at least close enough to pay attention to what else he had to say.
I don't know how his formula accounted for geopolitics, advances in retrieval methods or factored in the ways we might alter our behavior in response to recognizing that supplies are limited. But he's probably worth paying some attention to. Although, I was under the assumption that he predicted peak global production for sometime around the turn of the century, so he's already off on that one.