Yeah, its pretty great. I picked the first one up on a fluke and couldn't put it down until I finished the whole series. He writes very believable characters who are complex and interesting, even the ones I don't like. I think Inevera is one of my favorite characters in a long time.
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It was also implied/suggested that demons weren't really supernatural so much as life that evolved down in the chambers nearer to the Core, so over however long it took they were just completely suffused with magic, as that was their natural environment. That sorta makes the Core neutral and, while certainly evil, demons (at least those not of the Mind Court) are just critters.
Its just more interesting to me that the Core isn't like "hell".