This is often considered to be Heinlein's best book and it is certainly one of his best. It is probably the most archetypal Heinlein novel.
The book concerns a revolt on the moon and is yet another restatement of Heinlein's philosophy of radical libertarianism. It's interesting because it has a central incoherence, often found in radical libertarians, of insisting that the government should not interfere with the decision making of individuals, combined with an almost complete contempt for the decision making capacity of those individuals. It is none-the-less, after Starship Troopers, the most interesting statement of his philosophy.
Heinlien invents a future way of speaking which is handled barely adequately, but the rest of the book is well done. Well plotted, always extremely readable, with interesting, albeit totally un-lifelike, people. The character of Mike is along with Hal from 2001 the most interesting AI I have ever come across.
Heinlein at almost his very best.