Very disappointing: 2.5* (it's not terrible, but it's weaker than books I award 3*, and I enjoyed it far less).
I know of Heinlein as a sci-fi author and had heard of some interesting language-type things that make this novel unique, principally a Lunar dialect.
Although it's mostly set in a lunar prison colony, just over 100 years after it was written (and 60 ahead of now), it's more of a political story, and the Lunar dialect is just a slightly stilted pidgin whose most notable features are the omission of articles and pronouns, and the odd Russian-influenced word.
GOOD START, BIG IDEAS
It starts off promisingly, immediately introducing big issues around artificial intelligence. Mike (short for Mycroft Holmes, Sherlock's brother) is a supercomputer who enjoys jokes and playing pranks, which is an entertaining concept, but does he also have self-awareness, free will, emotions, personality and so on?
The other principal character is Manuel (aka Mannie and Man), who is Mike's chief programmer and engineer. Oh, and a stupidly named woman, Why Not (albeit spelt Wyoming Knott, but usually abbreviated to Wyoh).
Then it threw in issues of prison, punishment, freedom, civilisation, redemption, and some of the practicalities of living on the moon (low gravity, habitats, air, economics). Oh, and different types of marriage necessitated by a society with a huge gender imbalance: polyandry, clan marriage and line marriage (though the details and differences were not clearly explained).
In this community, the scarcity of women gives them more power in relationships, which is a nice idea, but the opposite of what seems to be the case in China, decades after their one-child policy was introduced, with reports of young women being abducted and forced into marriage.
Most of the humans living in tunnels on Luna are free: either the descendants of deported criminals, or they have served their time. In either case, they are too acclimated to return to the high gravity of Terra. There is no need for actual prisons, or even laws, because there is nowhere to escape to. The main industries are ice mining, and hydroponic farming; for the latter, they import fertilizer from Terra and then export the grain. But why go to the expense of all the transport to and from Luna, when they could do the same in tunnels on Terra?
POLITICS, COLONIALISM and MORE POLITICS
Understandably, some of the Loonies (as they call themselves) want independence from the exploitation of The Authority and its Warden, sent from Terra.
Cue LOTS of socio-political... stuff. It's not a long book, so I ploughed on, assuming it would return to form, but it didn't. Instead, I read endless discussions of political theory and tactics (it's all about the cell system and money laundering), meetings and diplomatic missions, and eventually war.
There are plenty of parallels with GB and Australia, but nothing startlingly original.
One thing Heinlein did get right was the fundamental importance of communications, including mobile and covert - and also social media (not that he called it that, but irreverent propaganda was used to undermine the Authority and create unrest).
However, everything seemed too easy. Mike was such a super supercomputer, and he had no competition. I kept waiting for something dramatic and unexpected to happen, but Mike was TOO omniscient and omnipotent for dramatic tension.
A few final paragraphs tried to bring it full circle, by contemplating computer consciousness and emotions, but it felt forced and rushed.