This is my absolute favorite of the trilogy because of the complicated quests the various characters set out on before they eventually come full circle. There is a clear path as the story matures and more adult themes take the stage, leading to hard choices and confrontations.
This is, of course, the final battle, the big showdown between unicorns and wyverns and when even dragons enter the mix, it just enters a state of ecstasy for me. The eventual revelations and choices of the main characters wrap the whole saga up, nicely.
As with the two predecessors, I can only recommend this.