I think he's got the best handle on the implications and consequences of Peak Oil of any popular commentator out there. I know he has detractors on a couple of fronts: his articles during the last Lebanese unpleasantness didn't win him many friends, and on the implications of Peak Oil he's seen as being "too gloomy" by many. I have no opinion on the first issue, but as far as his gloominess goes I think he's actually just realistic. In fact, I think he deliberately soft-sells his real opinions because the depth of pessimism that is supported by the facts and an understanding of human behaviour can lead to paralyzing despair.
I know my pessimism runs much deeper than anything Kunstler has said in public. I was born, raised and spent most of my my adult life as a techno-utopian who believed that human ingenuity and the scientific method could overcome pretty much any obstacle. I now understand that there are some problems that don't have solutions, and I am convinced that we are facing one of them.
Where I'm actually a bit more optimistic than Kunstler is in my ability to look beyond the coming decline in industrial civilization to the inevitable cyclic re-forming of of some new kind of human society. This outlook is informed by my reading in the areas of complex adaptive systems, adaptive cycles and resilience theory. I talk about that a bit
here on my web site. It's the one thing that allows me to avoid those "long dark nights of the soul" that washed over me when I first grokked the box we're in.