The outstanding feature of this novel is its eerie prescience.
"In what is considered one of his most hair-raising, thought-provoking and outrageous adventures, the master of modern SF tells the strange story of an even stranger world -- 21st century Luna, a harsh penal colony where a revolt is plotted between a bashful computer and a ragtag collection of maverick humans..." - from the back of the Ace edition.
You can also read the article on Wikipedia if you're looking for more details.
This novel is a Prometheus Award winner (for libertarian science fiction) as well as a Hugo Award winner, and it certainly isn't difficult to see why. Consider, for example, the following nugget of wisdom:
Must be a yearning deep in human heart to stop other people from doing as they please. Rules, laws -- always for other fellow. A murky part of us, something we had before we came down out of trees, and failed to shuck when we stood up. Because not one of those people said: "Please pass this so that I won't be able to do something I know I should stop." Nyet, tovarishchee, was always something they hated to see neighbors doing.
If there's one thing that comes through loud and clear in Heinlein's tale of Lunar revolution, it's his long-standing belief that government should be small enough to enable one to "drag it into the bathroom and drown it in the bathtub," as the old quote credited to Grover Norquist puts it. In fact, Heinlein - through the character of Professor Bernardo de la Paz, a self-proclaimed "rational anarchist" - even goes so far as to propose that we abolish all compulsory taxation. "There is no worse tyranny than to force a man to pay for what he does not want merely because you think it would be good for him," the Prof states.
Well -- as a conservative Catholic, I'm not prepared to embrace Heinlein's deliberately extreme position on the role of government 100%. I think his system is especially vulnerable to break-down when it comes to the social order. In my observation, allowing "consenting adults" to do as they please without regards to, say, family stability ultimately leads to a more intrusive government and less freedom in the long run.
On the other hand -- "TANSTAAFL!" needs to be tattooed on every Congress-critter, Senator, and bureaucrat in Washington D.C. There is indeed no such thing as a free lunch -- or free health care, or a free education, or a free old-age pension. When our government declares that, for instance, well-woman care will henceforth be free, what our leaders really mean is that someone else will pay for it. The gynecologist responsible for that care, for example, will be forced to accept the government's standard reimbursement even though it's very likely that said pay-out will not match the fair market price for his expertise. The word "free," in a sense, is a declaration of war -- it pits some citizens against others and should therefore be used very sparingly (if at all).
The other thing I find strangely compelling about this novel is its pessimism in re: democracy. As the intellectual head of the Free Luna Movement, de la Paz does everything he can to ensure that the revolution is not influenced by the "democratic process" in any real sense. He rigs elections and effectively quarantines the "yammerheads" because "in past history popularly elected governments have been no better and sometimes far worse than overt tyrannies." Now, I dearly wish I could blithely dismiss this viewpoint, but I don't think it's entirely wrong. There's an old quote of uncertain attribution which states that "a democracy cannot exist as a permanent form of government. It can only exist until the voters discover that they can vote themselves largesse from the public treasury. From that moment on, the majority always votes for the candidates promising the most benefits from the public treasury with the result that a democracy always collapses over loose fiscal policy, always followed by a dictatorship." Well, I think the entire West is now struggling with this precise flaw -- and apparently, Heinlein saw it coming back in the mid-60's.
This is an ideas novel rather than a character-based novel. That being said, only a few of the supporting players struck me as flat and poorly written.
The plot didn't grab hold and throttle me, but it was solid nonetheless.
Heinlein's political conclusions are very provocative -- but not necessarily wholly misguided. See above.