[ Some spoilers follow...]

If I had to summarize my reaction to this book in one word, that word would be "boring."

I have to respect an author who tries to do genuine "hard" Sci Fi. For me, this means, first and foremost, ***NO FTL!****. Keep the action entirely within the solar system, and try to depict space flight in a realistic way. Bova did this well. Putting life on Neptune might be a bit of a reach, but I guess I can accept for the sake of argument that some sort of extremophiles might evolve there. So this book scores points for being an honest attempt at Hard SF, and I do like Bova's descriptions of the planet Neptune.

The problem is that science fiction is just that: fiction. Stories. They can either be "serious" stories, intended to reveal some important inner truth about life, fate, human nature, etc., or simply stories intended to entertain. And on this count, I think that Neptune is a clear failure. Its characters are dreadfully two-dimensional. It's as if they were selected from some catalog of Jungian archetypes - the Charming Rogue, the Haughty Princess, the Earnest-But-Inexperienced-Youth - and simply dropped into the story without any further attention to giving them any depth.

Apart from this, I thought that the development of the plot was very sketchy. When the protagonists found wreckage on Neptune and concluded that it was 2 million years old and of alien origin, my reaction was "wait a minute, how do you reach that conclusion?" There's a tiny bit of mumbo-jumbo about radioisotope dating and the metallurgical composition of the metal of the wreckage indicating that it was't crafted on Earth, but it was very sketchy and not at all convincing. And given that it's established in the story that the Neptunian fauna like to absorb various metals, sort of like vitamins, even to the point of eroding a ship's hull, I have to question whether conclusions based on metallurgical analysis should be accepted without careful consideration. On the strength of what was presented in the story, I couldn't blame the authorities on Earth for being skeptical: extraordinary claims demand extraordinary evidence.

Then came another "What the hell?" moment, again delivered in just a paragraph with little or no exposition.The aliens who left wreckage on Neptune had also long ago exterminated an intelligent and civilized race on Uranus. None of the protagonists were aware of this, but the news was delivered briefly, in passing, in just one or two short paragraphs, with no further comment. Isn't the existence of another sapient race - even if it originated in our own solar system, and even if it's now extinct - rather a big deal? If you're going to inject something like this, it demands some exposition, detailing how and when that now-extinct sapient species on Uranus was discovered, what it was like, and what is known about its civilization, not simply, "Oh, yeah, there were civilized aliens on Uranus, but they were wiped out by the same aliens who left wreckage on the surface of Neptune." All of this reminded me of the flaw in A. E. van Vogt's writing that Damon Knight highlighted in his well-known essay "Cosmic Jerrybuilder", in which he pointedly chided van Vogt for repeatedly introducing monsters, technology, or alien cultures simply by mentioning them in passing, without any further description or explanation.

To be fair, Bova died in November 2020, and Neptune was published in August 2021. To me, it reads sort of like a rough draft. Perhaps if he had survived, he might have made further revisions that would have fleshed out this skeleton in a more satisfactory way. But as it stands now, I can only say that I found Neptune a real disappointment.
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