For me, this is the best of the series.
Sure, the first one gets the fun of defining the world and the plot for the reader, and the third gets the big finish.
But this one is the story of Elora Danan growing up. The central plot is a fairly standard mythic arhetype, but it provides a perfect hook to permit Elora to move from spoiled brat to perhaps understanding how she can be the prophesied Saviour of the Realms, and it does it in a most unexpected way. Dougay is a fine creation, and although there are times when he gets annoying, this is actually in keeping with who he is (in the same way that Rool and Franjean work well.)
Again, the descriptive work is excellent, the expansion of the world continues (Sandeni is very well realised) and the narrative flow fits together cleverly so that the reader can stay just far enough ahead of the characters whilst still being properly surprised. And the big revelation at the end is a genuine shocker, whilst still making perfect sense out of everything we have learned.
In passing, let me note that this book comes with a little Venn diagram at the front, showing the Twelve Realms and how they interact and relate to one another. Now I have to say that I wonder if there was a change between the first volume and these last two, in order to make the big finish actually work. Given that one of the threads is that all the Realms should have been present at Elora's Ascension, it's abundantly clear that although one is significantly absent, there are two others that are only present by implication (death, in the form of the death of a significant presence, and despair in the sense that the Ascension was flawed.) It is strongly implied that there should have been physical manifestations of all the Realms, but that would be tricky for those two. And, of course, the whole issue of Chaos/Demons is skipped over entirely - are they a Realm, or are they outside the Realms? I'm still not entirely sure...
Anyway, that's beside the point. This is the highpoint of the series for me, because it gets to have fun - it doesn't have to resolve anything, the characters grow and evolve and the plot can take a bit of a backseat whilst still being important.