So let’s do a little thought experiment. Start with a movie that’s bordering on the line between “fluffy but fun” and “kind of trashy, really” — say, Michael Bay’s Transformers. Now ask yourself if you’d want to watch the same movie again from a different POV — instead of focusing on Shia the Beef, it’d be all about what Megan Fox was doing throughout the movie. It’s still the same story and all, but you’re just seeing it from a slightly different angle and some of the fluffy side stuff is marginally different.
Does that sound interesting? Then you should totally read John Scalzi’s Zoe’s Tale , a retelling of The Last Colony from the point of view of the teenage daughter of the other book’s protagonist. If not, though, this is thoroughly skippable.
Which is a pity, really, because there’s a decent sf/fantasy tradition of interstitial YA novels. Take Anne McCaffrey’s Harper Hall trilogy, which takes place during the same time period as the original Dragonriders of Pern trilogy; or Dave Duncan’s King’s Daggers books, which take place in between the King’s Blades.
But the key to making a successful interstitial is to use the events of the main story as background while telling a smaller and more personal story. The result tends to be about coming of age in a turbulent time, with the plot events of the main series providing the turbulence. (Arguably, John Ford’s Growing Up Weightless is the YA interstitial taking place during a book that was never written.) This works well because it means you don’t have to retcon world-changing stuff in the YA series into your main book, and because it avoids feeling like you’re just telling the same story twice.
Alas, Scalzi’s didn’t do that. He did tell the story twice, and he did have to retcon events into the main books (”Okay, guys, when we get back to the colony, we have to never tell anyone about this ever, not even my parents, even though that makes no sense at all for our characters.”), and the result is not at all successful.
It’s possible that there’s a reasonable short story lurking in here about Zoe’s time with the Obin (which was badly undertold in the real book), but the rest of it is just pure, unnecessary filler.
(Oh, and for people wondering how well Scalzi writes a teenage girl, the answer is pretty well, assuming the teenage girl in question sounds exactly like John Scalzi.)