This is not the most original work of science fiction. If you have read Ringworld (S.F. Masterworks)
you'll be amused by the similarities here; the titular artifacts in each book are, in some ways, so similar that Shaw can only be encouaging us to compare Ringworld and Orbitsville. Perhaps then, this is a parody, much like Pratchett's Strata
? Maybe. There are certainly aspects that Shaw dwells over, which Ringworld was criticised by reviewers for missing out, such as believable female characters and some sensible explanation of what the big, silly, pivotal object was actually built for.
In this latter case, Shaw actually manages to formulate an appeailng answer, perhaps even the punchline that the whole book was written to set up; as this is made explicit only in the last revelation of the book, I won't spoil it.
The story itself is a fairly linear hard SF adventure with a sparse cast of characters that succeeds because of its breathless pace and a grandiosity that recalls Samuel R Delaney. What is particularly effective about this novel is that Shaw manages to maintain the sense of adventure at the same time as doing a lot of scene-setting and made-up science, a balancing act that better known writers have failed at, and he achieves with only a couple of wobbles.
There's no real surprises in the storyline; the lead character and villain are well-drawn but develop very little, the action reaches a couple of nice peaks of jeopardy, but our hero is too traditional to die easily. All in all, this isn't a book about theme or narrative. It's about the scientific concept and there's plenty here to amuse the hardest SF nut.