I loved Angelfall. I loved World After.
I liked End of Days.
The heroine Penryn and all her companions return in this last book. I read this book in two days, and there were lots of new monsters, lots of "Oh, no, you didn't!" moments, and new emotional territory for Penryn that was more precarious than her surroundings. But...
But this longer book felt like it didn't have quite enough content to fill it, which is odd, given its lush-for-description Apocalyptic theme. The plague that could be contracted immediately just by being in the vicinity of the carrier also threw my toxicology-and-epidemiology-sense for a loop. And the ending is very, very pat, wrapped up, and happy, which is also odd, given the lush-for-sorrow theme.
Lessons for writers: I know a certain format is expected of stories, especially to get published these days, but I don't think it should force your themes to go against themselves.
But I would certainly read more from Susan Ee.