I have actually read a few of these. I quite liked the ones I read, and while i'd agree that they would probably appeal to the YA market, they're not exactly kids books. They are, of course 'fantasy in space' as opposed to SF, but that is understood with SW I guess. There are various books that slot in before or between the prequel film trilogy and I've read these. James Lucino has written a few (e.g. Cloak of Deception and Labyrinth of Evil) which are very readable. Lucino is not a bad author. I've also heard good things about many of the books that come after the films too, most notably The Thrawn books by Timothy Zahn and the Jedi Academy trilogy by Kevin Anderson. These come recommended by many and may be worth checking out (though I've not read them).