I don't think it is funny, in the belly-laughs way. Instead, it is interestingly bizzare. It is the iconic book of conspiracy theory.
I think the pretension others see is, in fact, part of the fiction. When a major point of the book is that most people do not know how much psychadelic wierdness actually runs the world in which they live, of course they'll look pretentious. Anyone who claims to know more than you looks like he's trying to be superior, right?
And, I figure the "only get it if you're hip" comes from the fact that back when it was written, hip people did drugs, and much of the book reads like a rather cogent and vivid trip on recreational pharmaceuticals. So, it is more like, "only get it if you're sufficiently stoned".
There is, buried in all that, quite a bit of actual philosophical content as well, if you can look past the trappings.