They are basically post-apocalyptic fantasy. Not fantastical at all, which is one of my favorite parts. Something normal to read between the fantasy movers (of the universe) and shakers (of the storyline)!
I reviewed The City of Ember, probably would have a problem doing The Prophet of Yonwood, it's kinda bleah. The People of Sparks is better written than the first one (and the third one), but the conclusion it comes to is less that satisfying from a Christian perspective. Not as a atheism type of thing, but the main characters decide to ****SPOILER!!**** love their enemies, just because if we all love, that will prevent bad things. Oh please. ****END OF SPOILER!!****
I'm really enjoying the fourth one, though. I have maybe a third of it to go.
So there's your crash course in the Ember series.