This is the second Baxter book I've read (after VACUUM DIAGRAMS), and like the first it's a mix of brilliance and disappointment.
Baxter unquestionably has the wildest hard-physics imagination in the business. The world depicted in FLUX is a staggering conceptual achievement, taking the amazing concept of neutron-star life first suggested by Frank Drake and developed by Robert L. Forward in DRAGON'S EGG & STARQUAKE and going one step further, creating an ecosystem within the neutron-superfluid mantle of the star and exploring its whole geography from crust to core. The biology, locomotion and senses of the inhabitants are well worked out.
But Baxter's imagination tends to outrace even him. In both his books I've read, there have been major flaws in logic, points on which he failed to think his ideas through. Here, for story convenience, he asserts that the nuclear-size humanoids' life and thought processes happen at normal human speed. Readers of Forward will see the absurdity of this. The nucleonic processes on which this life is based are a million times faster than chemistry, because the particles are so much closer together. Even if it were possible to slow these people's life cycles so much in proportion to the underlying processes, they'd be agonizingly slower than the native organisms around them, living on a slower timescale than even the plants. There are other moments of shortsightedness; sometimes he describes them in humanlike ways incompatible with the anatomy and physics he's defined. (How could Dura have "slick palms" when they don't perspire?)
When the reason for these micro-humans' creation is finally revealed, it doesn't make sense. It would've been more logical to build mindless robots for the task, and ones better-designed to fit the environment. The creators' choice to make them almost exactly human down to the same impractical anatomy and the same emotions and aspirations shows a sentimentalism fiercely incompatible with the project's goals.
Baxter also gets confused about the scale of his trademark structure, Bolder's Ring. In VACUUM DIAGRAMS he said it was millions of light-years across -- yet described an attack on its rim affecting its center instantaneously, and described a distant observer seeing the battle across its whole width in real time. And here, he describes it appearing tiny from a distance of mere thousands of light-years. Baxter seems to have trouble realizing the physical and temporal scope of his own creations. His imagination is bigger than his judgment.
Baxter's a far better writer than Forward, but as in Forward's books, the plot is basically an excuse for illustrating the environment and physics. His characters have a modicum of emotion and personality, unlike Forward's, but are sometimes superficially drawn and hard to get a handle on. The one sexual interlude is painfully awkward and gratuitous from a character standpoint, serving only to illustrate the mechanics of the act for this species. (And let's not go into Baxter's seeming obsession with bodily functions. He could've chosen a more pleasant term for biological jet-propulsion.)
Amid the superlatively exotic setting, the society is relentlessly ordinary and unimaginative. The sociological storyline replays the mythology of countless British WWII films (and American films about Britain, such as MRS. MINIVER) -- a stratified society is torn apart by disaster and becomes united, promising to rebuild as an egalitarian utopia. It's tacked on quite awkwardly here. Overall, Baxter pulls the reader in two different directions -- in the environment and physics he strives for unimagined wonders, but for the people and society he pulls against that and forces them to be as mundane and familiar as possible.
FLUX portrays the most extraordinarily alien, yet credibly developed, physical environment I have ever seen in SF. But this just throws the book's flaws and its ordinary storytelling into sharp relief. And Baxter's failure to think through all the ramifications of his own ideas, and the huge logic gaffes that result, are a continual frustration.