If you haven't seen "The End of Time: Part 1" yet, there's a spoiler ahead.
I've been watching the previous Master trilogy ("Utopia"/"The Sound of Drums"/"Last of the Time Lords") both in preparation for "The End of Time" and as research for another post I'm writing.
So, as silly as I thought the "Master race" cliffhanger was, given how the Master was defeated in "Last of the Time Lords," it's actually kind of genius. The Doctor restored himself (as silly as that was) using the focused psychic energy of the vast majority of the human race. Now, the Master has become the human race, not only eliminating them as potential allies for the Doctor, but also providing himself with some of the means to supercharge himself with the focused psychic energy of billions of people. Although there's always the chance that it wouldn't work, or that it'd be spread out over billions of Masters, but it's either a very lucky or very clever solution.
Also, while some seem to be bothered by the "Secret Books of Saxon," I can't say that I am. After all, the Master ruled the world for a whole year; he had to do more than just humiliate the Doctor, order the Toclafane to kill humans, and smack around Lucy. It's fitting, given his past and his obsessions, that he'd spend a good chunk of time seeking immortality and looking for ways to extend his lifespan and plan for his own death. After all, that's been his schtick since day one.