Why is his correlations with body types laughable? The correlation between body types and various psychological manifestations is well documented and a valid type of research in modern psychology. The enneagram divides types into body, heart, and head types and Sheldon similarly divides human bodies into types where, for example, ectomorphy is being focused on the nervous system and the brain. And there is a predominance of ectomorphy among the head types.
I got my basic picture through a combination of Naranjo and Almaas, actually. I find it difficult to empathize with other types, and to convey the human dilemma in my own, without referring to a loss of an idealistic notion that is ironically still fixated upon. Imo, Almaas covers this issue the best of all sources I've seen, his student Maitri being a decent second option. It's not a very good starting point for self-reflection though.
On the other hand, diagnosis of the deeper pattern of problems is probably clearest by Naranjo's C&N.
Well, to give an idea, Almaas's work centers around the issue of basic trust (or more to the point, loss of basic trust as being fundamental to the loss of essence). Everything in his book, especially when it comes to the elaboration of the Holy Ideas themselves, is written in terms of his personal philosophy. Most people, myself included, are given the impression that he goes to great lengths to explain something that could be conveyed in a fraction of the writing; however, I think if you did, you'd inevitably be elaborating the issue from a dualistic perspective, which is at odds with Holy Truth. Were you to internalize his way of seeing things, you could very well reverse the loss of basic trust (though to actually do that takes more than simply reading his work).
On the subject of his philosophy, note that Facets of Unity is precisely what it sounds like: a book about 9 facets of reality (as experienced by "enlightened consciousness" a.k.a. from an "objective view"). It is secondarily about the Enneatypes. Yes, he elaborates on each type in terms of specific difficulties and delusions based on the loss of the Holy Idea, but this all maintains the perspective of from the Holy Ideas. It can seem very removed if you don't understand how your development is a manifestation of what he describes, and even then I'm not sure it really follows. (For example, it took quite a while before I could recognize how my 9-dilemma could be an inferiority complex. I wasn't even defensive; I just felt like it was off until I really looked, and I still feel it misses the point.)
On the other hand, it's exactly for this reason that I put him on par with Naranjo (and find it impossible to say one or the other is my favorite). He doesn't paint a picture for you of what the type is like, but that's more the realm of the ruling passion. Each type is fixated on one of these ideas and responds to a loss of that idea. It's one of those "call it what you like" sorts of things. You understand what the Holy Idea is and how it can be lost, you have a feel for the type's core dilemma. How the type reacts to that is an open-ended question, even if there are strong trends (i.e. ruling passions).
Anyway, that gives you an idea of what to expect. I don't really subscribe to the notion that these are objective views of reality (I'd argue they're just the naive, childish notions beaten out of us by reality), but I think this book sets a great palette for how people come to develop their enneatype.