I was really having a hard time getting through The People of Sparks, and I was not excited about reading the next two books. I have to say though, I was pleasantly surprised by The Prophet of Yonwood.
I think I really just hated Lina and Doon. Nickie, on the other hand, was nowhere near has annoying. Although she had her flaws, all she really wanted was to do something good and help the world. The characters weren't well developed, and the plot was only so-so, but I think that this Book of Ember was a nice read for what it was. It didn't take me 6 months to finish it either, so props to it on that.
I'm not really sure it was entirely necessary as part of the series, although it was interesting to see all of the pieces fall into place with "The Builders" and the woman who left behind the journal. I also don't really agree with the order in which they were written/published, since I think it's really weird to have two books, then a prequel, and then a sequel to the second book. Maybe that's just me though.
While I really, really hated The People of Sparks, I would definitely encourage a middle-grade reader to get through it so that they could read The Prophet of Yonwood. Or I might just tell them to skip The People of Sparks entirely and have them read this book first.
This book definitely deserves a 3/5, since it was good for what it was but could have used some more depth and a better plot. And it's also a little young for people in their early-mid twenties to be reading. Give this to your elementary/middle school kids, and they'll love it.