Geoffrey McKinney has his finger on the pulse of D&D.
This is very specific — I don't necessarily means that he captures any timeless essence of D&D (although, to be fair, he certainly does), or that he betrays a startling grasp of some recent edition. I mean he truly gets the spirit of the Little Brown Books in a way you don't often see. This may not be your vision of D&D — hell, I'm not saying it's mine, for that matter — but he definitely understands the exploratory, puzzle-laden weirdness of D&D as codified by Arneson and Gygax.
Understanding those roots are important because they're really the bedrock upon which the hobby is founded.
Plus, he makes magic truly mysterious in a way I've rarely seen in D&D. Magic is the purview of weird, obsessive forces in World of Darkness and Unknown Armies, but it's all too easy to fall into the trap of "Ho-hum, another magic missile."
It's really something I've been missing in my current delve into D&D, and I'm glad to see it again.
Magic is stranger and more special when it takes the "How far are you willing to go for power?" aesthetic of Carcosa or the "I've been studying one spell for fifteen years at the exclusion of all others so that I am now the absolute master of all trees in this grove" aesthetic of Isle of the Unknown.
Really, it's Unknown Armies for D&D — magic is a strange, idiosyncratic art that pushes those who follow the path away from the common world we know.
Magic envelops you in a cloak of the Weird.
I hope we see more stuff from him in the future, because he's one of those guys on my "Hey, I want to buy your stuff!" list. At the very least, I hope some of his design philosophy rubs off on the rest of the industry.