I enjoyed the trilogy, but each book felt weaker than the previous one. While the first two books may have merited 3.5 to 4 stars, I'm not willing to give this one more than 3. Modesitt has a knack for creating interesting worlds and supernatural frameworks, but he's just not as good at spinning a yarn about people. Concretely, the following things turned me off:
* The ending of the book will be evident to any observant reader, and should have been obvious to one of the main characters (Dainyl) as well, since he himself caused something similar. The combination of warnings from the ancients, previous events, and the glaring weak point of Ifrits on Acorus should make this all blindingly clear to anyone who takes five minutes to think on the issue.
* The characterisation of villains is almost comical. Invariably, they are petty and self-interested and succumb to misdirected rage that drives them to murder the main character. None of their enemies is shown in a virtuous light: if they initially seemed like reasonable people, they will grow an irascible, violent and utterly-selfish streak in a couple of chapters as they turn against the main characters. If they seem conniving, devious and self-interested, these traits will disappear if they align themselves with the main characters.
* Modesitt seems incapable of writing a good romance scene. Two characters are fated to be together, yet there are perhaps two or three scenes in the entire trilogy in which they show any chemistry whatsoever.
* Regarding the romance, the Soarers insist that these two characters getting together is important to the world. This is mentioned twice, yet nothing of the sort is ever shown. The next book set in Acorus takes place 200-300 years after this series, so unless the Soarers have the power of prophecy (and there is no reason whatsoever to assume that this is the case), this looks like little more than a plot device to encourage our young Majer.
* Action scenes tended to have a 'samey' feel. The campaign in Iron Stem takes place in a short time, in a landscape that is poorly described, and battles amount to Cadmian troopers setting up lines and shooting charging enemies down. This may be realistic, but the formula doesn't vary and it isn't interesting to read. Even Dainyl's battles become boring due to the way in which he mows down his opposition.
* Related to the above, one of the main characters persists in making use of a Talent which is alien to him, which others have warned him against using and towards which he himself is ambivalent, even when he has the alternative of drawing on a Talent which is native to him.