I have a confession: when I first read this book about 30 years ago I was so naive that I actually got to the final chapter still thinking the aliens were benevolent. Re-reading it last week I realise you are supposed to rumble their duplicity about half way through and the tension is about whether the humans will catch on in time. I think the plotting would be better if it had been written to support my initial reading. That could have been achieved by leaving out the alien-perspective passages and telling the Midshipman sub-plot in flashback at the end. Written this way, with a spectacular reveal right at the end, it would be a much more rewarding read.
This is probably the hardest story line in SF: first contact on the alien home-world. Not only do you have to imagine an entire alien civilisation, you also need a credible human future with star faring technology. This book manages the first and hardest part brilliantly but then lets itself down terribly by constructing the human civilisation from the most ridiculous assembly of sub Star Trek space-opera clichés this side of the Romulan home world! Somehow an alliance between the Soviet Union (excusable - this was written during the cold war) and the US has produced - the British Empire in space! Who would have expected that - an aristocracy! Just substitute planets for colonies, space ships for sea ships, magical faster-than-light "tramlines" for trade winds and job's done! It could have been amusing if they'd come up with a reasonable historical excuse for this, but they do not and you cannot help concluding it was just laziness. This ludicrous political landscape is populated by nationalistic clichés from old earth. I mean, there is not one but several Scots engineers with thick brogues (beam me up Scotty!); a paranoid and ruthless Russian admiral; a rebellious planet called "New Ireland" next to a loyal one called "New Scotland"; a corrupt and fabulously wealthy Arab merchant with a chip on his shoulder; a German character descended from a colony that recently started a war to impose its ideas of racial superiority. I could go on, but I risk someone trying to defend this tripe as homage!
However the inventiveness of the alien civilisation makes up for this in a big way. Believable and genuinely alien aliens are so rare in SF, and the "Moties" are really different. Their biological imperatives are alien, their history is alien, their physiology is alien, their reproductive mechanisms are alien, their politics is alien, their technology is alien, their motivations are alien, their architecture is alien, their situation in the universe is unique. And all of this is imagined from scratch rather than mix-and-matched from human templates, and fits together all of a piece. The best part is that they are not either good or evil, just driven by the imperatives of their situation and placing their own interests first. It is a truly amazing achievement, quite unique in my reading experience. On top of that the authors have come up with a really clever plot device to allow the reader to totally empathise with these aliens.
Because of the superb "Moties", I give this poorly written, badly plotted, cliche ridden book a full four stars. It is very tempting to conclude that the authorial team comprises a very imaginative, creative and brilliant scientist hitched to the worst kind of SF hack writer who wouldn't get published in any other genre.