"The Wishsong of Shannara" opens in Autumn, and it is an autumnal work. Something is fading and passing from the Four Lands. This something is Allanon. The demands of keeping the Four Lands safe have aged him, and the Druid is but a shadow of his former self. He even complains that no one recognizes him when he first appears to the Omsfords. We also know that he has begun to experience failure and a loss of his powers as the Mael Mord has thwarted his attempt to destroy the Ildatch. All this is to say that Allanon, the only constant character through the first three novels and their prequel, is dying. This stands out all the more when we look at our youthful cast who seem aged 14,17, and 18, respectively (this should also give us a clue as to who Brooks' perceived audience is).
Nature always reflects plot in the world of Shannara; a lesson learned from Tolkien. Our plot is also autumnal. No grand clash with evil is promised, no chance for heroic sacrifice, just a quick "get in, get out;"
a twilight struggle for a twilight age in which the last of the Druids is dying.
All of this, of course, impacts mood. The overall mood of the novel thus far is quiet and sad, even though the pacing is quintessential Brooks. The youthful heroes are teenage friends in exactly the way I remember teenage friendship, but they do not lighten the sense of failure, desperation, and passing.
Some final thoughts and that will be that. This book has a clear, compelling tone that is lacking in "The Elfstones of Shannara." Brooks starts the novel on top of his game. As the art cranks up a notch, however, it also exposes some of the weakness of Brook's underlying machinery. We can already see clearly within the first forty pages that the Shannara novels all follow the same formula: Allanon appears to teenage Ohmsfords telling them of an impending crisis which only they can overt by magical means and wins them over after a brief initial resistance then taking them on a quest which opens up more of geography on the map of the Four Lands (North, West, East, respectively) resulting in a victory but also exposing Allanon's deceptive and manipulative tactics. We also begin to see that the Ohmsford heroes will always be teenagers (both Bilbo and Frodo, by contrast, are in their fifties when they set out, though Sam, Pippin, and Merry are all younger) as the novels are primarily serial novels for teenagers (age 12-16 at a guess). This sense of formula and repetition necessitates the death of the series and its relaunch if the quality is going to continue to climb. Brooks seems to have sensed this too, and "The Wishsong of Shannara" is the last book in the original trilogy. A discussion of whether Brooks makes any improvements will have to wait for a read through the Heritage of Shannara series.