If you want some more mature books from Piers Anthony, the Apprentice Adept series and Incarnations of Immortality series are better than the Xanth ones. Plus,

If you want some more mature books from Piers Anthony, the Apprentice Adept series and Incarnations of Immortality series are better than the Xanth ones. Plus, they're both only 7-8 books long, so it won't take you forever to read them all (if you actually get into them). Apprentice Adept is kind of a cool dual-world series, with sci-fi in one world and fantasy in the other, and the ability for some to move between them. You should start with the first in the series, of course: Split Infinity. Incarnations of Immortality also has the juxtaposition of sci-fi and fantasy, but in one world. The "hook" for this series is that the major "forces" in the world (time/death/fate/war/etc...) are actually offices which people fill (think The Santa Clause, but without Tim Allen or christmas). The first book of the series is On A Pale Horse. A final word of warning: I read both of these series a long time ago, so it could be that they're actually not as mature as I remember =)