Orbital (a dull name, like a place holder name they forgot to change) is a hard science fiction, colonized solar system, no FTL campaign setting for Traveller. I have personally never liked the Traveller rules, considering them way too complex (especially in chargen), but bought the book because I have long wanted a hard sci-fi solar system based rpg. If you like Traveller, you will get everthing you want from this book. If you are like me and can't even finish the TMB, I see no reason why with a little adaption you could not use this setting with a rule set of your liking (there is no necessary connection between this universe and the Third Imperium). The setting is realistic, detailed, and well-written, but I have two major gripes:
a) the Luna/Earth Cold War. It is necessary, in the author's opinion, to motivate humanity to colonize the solar system, but I just find it hard to believe. Hard to believe that after only a few decades colonists on the moon would become so unalterably opposed to Earth and see themselves as so different from it. This division just seems unmotivated, existing solely to provide conflict/tension in the setting. A better division might have been Earth/Mars or Inner System/Outer System.
b) the book's organization. The chapter that describes worlds of the solar sytem and sets out its geographical/political structure should come before the chapters on organizations, space craft, etc., because they are hard to understand without knowing the geography and politics of the system.
Those problems aside, I rate Orbital as highly as I do because the information inside would be a invaluable resource to anyone planning a hard sci-fi campaign or writing hard sci-fi fiction.