My favorite Fabre: landscapes and turtles
My favorite Munk, if only because of how much greenburg on has to read in modern art criticism classes
I actually don't have anything to say about Ron Davis because I don't know him.
As for geiger, I'm pretty dismissive. Its a great vision, and very avant guard for decorative art, but as far as I've read, and based on my personal examination, there isn't much else to it.
Personally, I don't know how you can be a fan of highly conceptual art like Fabre's, or cool postmodern pastiche like Munk, and at the same time, embrace super literal, single subject, painterly stuff like Grey's.
He has one subject: altered/alternate states of consciousness.
He has one means of representing it: literally.
The reason he isn't held in high regard is because he only says one thing, and its something that most people in the art world understand, but don't regard as particularly important to their own art. That's why psychedelic art is dismissed: its "the best thing ever" to the same group of people who think tool is "the best band ever". By that I mean, loved passionately by people who are, if the past is any indication, going through a phase. Most people grow out of thinking of psychedelics as central to their lives, or their spirituality, or their aesthetic. I'm inclined to believe that the art of someone like Mathew Barney, in all its inscrutability, is fundamentally better than Grey's, because its more complex, and more nuanced. That's the same reason most people would say Pynchon is a better writer than Orwell, just don't say it in a room full of literate 10th graders.