Graham Harman is a philosopher associated with the new movement of speculative realism in Continental philosophy which includes thinkers like Quentin Meillassoux, Ray Brassier, and Levi Bryant, among others. Graham Harman is unique in pursuing what he calls an object oriented philosophy (actually, I believe Levi Bryant is now pursuing an object oriented approach as well). The entire movement tends to be a reaction against what they take to be the "anti-realism" of most Continental philosophy.
This book serves as a good, short, general introduction to Harman's object oriented approach. Harman makes many arguments throughout this book, but I think his fundamental arguments can be reduced to two general claims. First, the human-world relation is in no way special. As Harman continually reiterates, there is no difference in principle between the human-world relation and the relation between fire and cotton (or any other physical objects). Real objects withdraw from human access, but the same is true of cotton in relation to fire. Fire only reacts to certain qualities of cotton. The fire does not, for example, relate to the cotton's "whiteness" but only to its "flammability". This is what I find to be the most compelling aspect of Harman's philosophy.
Harman's second main argument is that objects constitute an autonomous level of reality. Harman is opposed to both "undermining" and "overmining" objects. Undermining is the attempt by philosophical materialism to reduce objects to a more fundamental level of reality (to reduce human beings to cells, and cells to atoms, etc.). Harman essentially argues for what is now known as emergence. It is a mistake to reduce humans to a lower level, but there are also objects, such as societies, that are larger than humans, and it is equally a mistake to reduce those higher level objects to human beings. Each level achieves a certain degree of autonomy, and the world is ultimately constituted by the relations between autonomous objects at different levels. Overmining, on the other hand, is what happens when empiricists reduce objects to independent sense qualities that are only unified within a human consciousness. This also annihilates the autonomy of the object, and makes the unity of the object depend on a unifying act carried out by consciousness.
Harman works out a fourfold structure that is loosely based on Heidegger's notion of the fourfold between: real objects, real qualities, sensual objects, and sensual qualities. Harman then attempts to explain the tensions and interactions between the members of this fourfold structure. To give only a single example, Harman argues for indirect causation, which means that real objects are never related to other real objects, but only relate indirectly to each other through the other three poles. What I found most interesting and compelling about Harman's fourfold structure was his brief taxonomy of previous philosophies each of which attempts to reduce all of reality to one pole within Harman's fourfold structure. For example, strict empiricists tend to reduce everything to bundles of sense qualities and deny any reality to the other three poles, scientific naturalism tends to consider sense qualities to be nothing but epiphenomena and tends to reduce everything to real qualities (mass, momentum, etc.), phenomenology reduces everything to sense objects or the intentional correlates of consciousness, while Aristotelian essentialism tends to reduce everything to real objects or unified substances.
Against all of these forms of reductionism Harman asserts a necessary tension between all four of these poles. Harman's philosophy is, therefore, a radically anti-reductionist philosophy. Harman writes that "Instead of embracing the reductive positions of the correlationist, the naturalist, the phenomenologist, or the classical realist, object-oriented philosophy gathers the grains of truth found in all four" (143). Harman is essentially providing a taxonomy of previous philosophies and attempting to point out their one sidedness. They each emphasize one aspect of reality while neglecting the others. I find this aspect of his analysis quite compelling. Harman is able to present a comprehensive philosophical standpoint that is able to account for the limited validity of other, less comprehensive, philosophical standpoints.
I do have some minor reservations about certain aspects of Harman's object oriented approach to philosophy, but despite my minor reservations, there is no doubt in my mind that there is a lot that is of great value in Harman's philosophy. Harman also is pretty liberal in his interpretations of previous philosophers. Harman's summary of previous philosophers can often seem overly simplistic or even wrong at times. However, Harman is not attempting to write a scholarly work on Kant, Husserl, or Heidegger, or any other philosopher. Harman is attempting to present his own original philosophy, and in that task he is quite successful. All in all, I would say this book serves as an ideal introduction to Harman's philosophy, and object oriented philosophy, in general.