Rawls has done a marvelous job condensing the theory first presented in his massive A Theory of Justice into 200 lucid, succint, beautifully-argued pages.
Since the work is essentially a restatement, any review must take into account the effectiveness of that which was restated. For this, I would like to mention one area that Rawls ammended; subsequently, I would like to comment on how this change provided a complete new hermeneutical framework for the book.
At its core, the theory proposed by Rawls is based on a Kantian understanding of human persons and human freedom. Any familiar with Kant's political philosophy will remember the concept of the 'transcendental self', the self that is so completely free of human encumberances and entanglements that he is actually and literally free. This person literally has an autonomous free will and consequently has the capacity to be completely self-legislating. This is, of course, necessary if a person is to abide by the categorical imperative. Kant believes that a person cannot be free unless his will--his capacity to choose--is grounded in something pre-empirical. Rawls seems to believe this too. However, he understands that the idea of the 'trascendental self' is so shrouded in the obscurity of German Idealism as to be unhelpful for the average person. So, he sets out to bring the self to the earth and give it an imaginable, even a empirical, basis. And this is the function of the original position: to bring Kant's 'transcendental self' to the earth and provide a basis for it. This should be kept in mind throughout the reading.
While I enoyed the book thoroughly, I have a number of issues. First, Rawls himself says that the work can be read independent of any prior knowledge, and I take this to be true. Nonetheless, reading Justice as Fairness without preliminary familiarity with A Theory of Justice is bound to make the reading considerably more difficult. The reasons for this are many, the most notable being that Justice as Fairness is a restatement of a theory presented in an earlier work. Its job, essentially, is to fill gaps, answer arguments, and provide clarification that lacked in the original version (not to be confused with the 'original position'). While Rawls alludes to the problems he intends to fix, it's almost impossible to fully grasp without a cursory understanding of A Theory of Justice.
In sum, the work is an excellent piece of analytical philosophy, one that is sure to be around for a while. Nonetheless, I would encourage anyone ready to dig into it to to read--or at least become familiar with--A Theory of Justice.