I thought the One was great, and I didn't mind that him and the Kelbrid weren't hinted at earlier in the series. It made last few chapters of the Beginning pretty scary, I thought. The scene where Ax finds the polar bear hair aboard the seemingly empty ship was seriously chilling. The One scared me, how he seemed so powerful and we knew nothing about him, and how he only appears in the last few pages of the series.
The confrontation with the One is the beginning the title probably refers to. I agree with sherrilina that the final battle was really the events aboard the Pool Ship and Blade Ship. All of that stuff I thought was so much more intense and interesting than the usual Hollywood-style final battle, with all the good and evil forces clearly marshalled against each other, and the side characters are pitted against each other and a few of them die while the main heroes fight the main bad guy and win and celebrate and mourn the fallen. Everything in The Answer was so intense and climactic and unexpected.
And KA did set up how the Yeerk Empire was weakening. Taylor summarized it nicely in book 43. The Andalite had finally launched their major fleet, and the Yeerks' strategy of luring it to the trap at Anati failed. The Hork-Bajir couldn't sustain the Yeerks, Leera and Anati and Earth were lost, the Taxxons were revolting, 17,000 Yeerks had just been slaughtered, and the two most reliable Vissers had both failed spectacularly. On top of that, the lower-ranking Yeerks were getting tired of the war and resentful of their leaders, who were picking and choosing those who got morphing power. And with morphing power, Yeerks didn't really have a desperate need for hosts anymore.
