I haven't made my introductory post yet, so before I comment I just want to say that I am not a writer (yet!) just an avid fantasy reader. Most of my comments are going to be from the point of view of someone who had picked this book up in the library/bookstore and flipped to the first few pages to decide if I want to finish it or not. I do see a lot of potential, and it looks as though you are already aware of several of the things that bothered me (too much information too fast, etc). The basic idea of someone hunting down a child necromancer/summoner is interesting enough, the world you have created feels "solid" (you portray it as possible enough that I am willing to believe it for the sake of the story, bearing in mind that there will be revisions of minor things), and someone summoning a soldier demon by mistake takes interest one step further; I am intrigued. Yet I do agree with a previous comment that I would expect more conflict in that situation than currently is apparent. Without it, I'm not sure I would remain intrigued.
Specific thoughts I had on a first read through:
It felt like it started just before the action instead of in the action. This is easy enough to fix, and I'm sure you will/would have gotten there in early revisions, but it's a killer for the girl in the bookstore.
"Why does this hunter need guns if he can sink an entire village?" -This question was answered when you portrayed loss of soul as a (quite serious) cost of magic, but was quickly replaced with, "If it costs him his soul, and he's a hundred and fifty some years old, how much soul does he have left? How many years has he been using magic? Why would he EVER use it unless it was absolutely and undeniably his only option? He used it just now, and I can't tell if it was his only option or not..." (Does this play into your master plan? I hope it does. I feel as if I have been given a promise here that, somehow, the fact that this hunter is both missing a portion of his soul and nonchalant about slicing off more pieces will become important later. If this wasn't your intent, you may quantify how the soul leeching works as the story progresses to put the reader's mind at ease...you may already have done so).
Many of my other questions I had as I was reading will probably be laid to rest with further fleshing out of details as you revise. Little things like, why has it taken the hunter so many years to find this guy, but pictures of him are easy to come by? You could let me ask the question and then give myself the probable answer, or you could flesh it out with a detail that it was from his government file/driver's license/surv. camera, etc.
Not sure if my POV is helpful or not, I am only a few episodes into Writing Excuses, but if nothing else I hope to encourage you; this idea is worth developing/finishing!