The series really gets good with Faith of the Fallen. Just make sure you have it handy when you finish Soul of the Fire because the ending of Soul kind of pisses you off. I read them as they came out on hardback and when I got to the end of SotF I was like, "That's it? You're ending the book like that? I am pissed!"
Oh and book 7 (Pillars of Creation) goes off on a huge tangent but the story gets back on track in book 8
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