There's part of me that longs for the days that the Doctor Who books were written for an older audience, and this book is no exception.
The introduction had unnecessary confusion, in some extraneous attempt to make the alien race seem more human than the humans on the junk planet. It didn't really help the story, especially since the secondary characters were written well enough—even over-the-top characters like “Dirk Slipstream” (who reminded me of Ace Rimmer with the voice and mustache of Terry O'Quinn). You might think the story is simply too much if you add in the Pioneer 10 cliché (that satellite gets around in sci-fi universes), overly-blatant anti-religion subtext, and the now common DW rush to the finish (comet hits in 100 minutes, Doctor's at the edge of an acid lake with a spear poking at his back, Amy's outside the enemy base, nanobomb's set to go off, and there's something weird in the Gobocorp ship. Whatever will happen?).
Fortunately, where Llewellyn fails with cliché and excess, he succeeds with dialogue and characters. He does a fantastic job of presenting the Doctor and Amy. The voices are spot on, and its easy to see them in this adventure. The Sittuun, the major alien race present in this story, were interesting, if not fully developed. Slipstream is obnoxious at first, but makes for an interesting foil as the story progresses.
Overall, the book is a simple read and the interactions between the Doctor and Amy make it worth picking up. Personally, I love the Matt Smith Doctor and Amy, and any opportunity to see them in action is one I'll take. This isn't the best Doctor Who book I've ever read, but it was good fun and I wouldn't mind trying another book by Llewellyn in the future.