Soarer's Choice is an acceptable but not great finale to the Corean Chronicles. Modesitt weaves an interesting tale of political intrigues with his characters but doesn't do a particularly satisfying job of tying that to the world he's created, meaning plot development and resolution leaves something to be desired. I take a star off for the overall plot and a half star for shunting one of his lead protagonists to a secondary role, but I'll round it up to 4 stars as the intrigues were interesting enough the first read through to keep me up past my bedtime.
The basic problem of writing a prequel is that the reader already knows the ending, which means if you're not careful as a writer you end up spending the majority of your plot on things that either don't matter or just seem contrived to get you to the beginning of the next book. (Think the Star Wars prequels: you suffer 8 hours of hell to finally get to the great last 30 minutes, and even then parts of it feel contrived.) Modesitt's actually been both very good (the first few Recluce books) and very bad (the Cyador novels) at walking this line.
Soarer's Choice falls somewhere in between. In this case, the prequel's problem is that at the start of the book we know that something was done to the life-sucking, planet-invading alectors by the ancients, but we're not sure about who, how, when, and what resulted, just that those questions have to be answered by the end of the book. (The why at least is nicely answered over the last couple of books.) The resolution of all these questions would have made a very meaty, intriguing plot.
Instead, we get a political drama surrounding the commander of the alector military forces, Dainyl, and a less-satisfying series of military battles with his native counterpart, Mykel. While Dainyl's ultimate moves are predictable for a Modesitt protagonist - when those above you don't get the problem (in this case keeping the alectors from killing the planet off for selfish personal gain), fix it yourself! - it's still one of Modesitt's better one-man-against-the-world stories in a while and worth the read. On the other hand, Mykel gets shunted off to a series of military battles that may be important to setting up the world of the sequels but have almost nothing to do with the impending ancient vs. alector struggle we know is coming. As a result, his plot line seems largely irrelevant. With character development stunted, even with vastly reduced stage time every time he shows up it feels like he's taking away from the main plot, not adding to it. The two plotlines barely interact, a shame given the effort Modesitt made in developing Mykel in the first two books.
The bigger problem, though, is that while we get answers to the what resulted and when questions we really don't get much of an answer to who and how. Dainyl's struggles end up being a very interesting story that is largely marginal to the bigger overall plot resolution, and Mykel's struggles add almost nothing. This would have been a far better book had both characters been a couple of the main answers to who, the plot focused on how, and Modesitt doing his normal great job with the moral questions that raises for both. Instead, the plot more or less just finishes and we're set up for the original three books.
Still, the Dainyl story is a good read and this is more worth buying than most fantasy books. With a different plot line, though, this could have been one of Modesitt's best, and that's a bit of a let down.