The first objection you may want to throw against Rawls is that it appeals to the lowest common denominator (I know I did the first time I read his work). Most of us agree that when it comes to justice, however, we should ignore from our considerations morally arbitrary variables over which we have no control, like race or age, for instance. One might want to conclude, therefore, that a truly fair system would be one based on merit and effort, but Rawls brilliantly points out that even a meritocracy doesn't go far enough in discarding morally arbitrary considerations of variables for which we have no control: even the naturally gifted can't claim credit for their success, since their success is based on factors as arbitrary as birth order. In a Harvard classroom full of students who most likely believe in a meritocracy, an impromptu poll hilariously proves Rawls' point :)
This analysis leads to a discussion of fair distribution of wealth, income and opportunities in which Rawls' egalitarianism must contend, in a truly fascinating set of thought-provoking arguments, against alternative systems of utilitarianism, libertarianism and meritocracy. Finally, and in order to drive his point home, Rawls draws an important and subtle distinction between desert and entitlements to legitimate expectations, and argues that those at the bottom of society are no less worthy simply because they lack the talents that their particular society happens to favor. In a truly just society, Rawls concludes, the naturally advantaged must share with the least advantaged.
Whatever conclusions they draw, this is how politicians should deliberate! :)
If you're curious about the birth-order effect, check out Charlie Rose and Stephen Colbert talking with Frank Sulloway about it.