Well that was an unexpected ending! sweet though.
Part of my speculation is due to the fact I have read a somewhat similar book, well series (The Cal Leandros series, which i adore)
These's books have a lot in common - Monster baby brother, big protective brother, messed up mother, intriguing love interest, great side kick.
The differences are:
1 - Cal fights his monstrous change 110% plus while he's a dick to pretty much everyone his affection for his brother is clear from the beginning. Cal and Niko have the better relationship. In The Demon's Lexicon it takes ages to grasp a decent understanding of Nick and Alan's relationship and you have to constantly reevaluate it.
Plus Nick favor's swords over guns - unlike Cal.

2 - The Big Brother, Allen. Allen and Niko are probably even more alike if you ignore the fact that Niko is much more badass (Allen is pretty awesome but you'll understand once you read the Cal Leandros books) He's also much better looking and he has this awesome Zen thing going on. Their both nerds which is cute. Allen is a lot more caring about others, though he will sacrifice others safety for Nick when push comes to shove, but unlike Niko he'll also go out of his way to help others. Allen also prefers a gun over a sword and he isnt as good with the ladies.

3 - The Mother Issue, I'm not even going to touch that.

4 - Same with the love interest - don't want to spoil all the fun.

5 The Side Kick - In The Demons Lexicon this portion is filled by an adorable young gay teenager, Jamie. Jamie is hard to define (though he was by far my fav character) He starts off as a victim to the demons, dude is pretty much doomed, even knowing all this Allen still wants to help, Nick obviously doesn't care. Jamie is shy and timid and sweet and naive - really all the things that usually tend to annoy me in a main character. He's easy to push around, startles easily, runs and hides often but under all this when push comes to shove the kid has a steal back bone. He obviously gets it from his sister, who's pretty cool. Plus the sister and brother have a fantastic relationship - Jamie just pulls this off, he's like a kitten, who on occasion brings out teeth and claws. Great kid.
In Cal Leandros series the side kick is the famous Puck (who i also greatly adore) but i don;t think i need to inform you how completely opposite to Jamie he is - well except for the whole liking men, Puck likes everyone.

Now onto the worlds, I personally prefer Rob Thurmans world better, I think she is the more gifted of the two writers, or maybe its just her monsters are more... frightening.... nightmare inducing is a good describing word.
Now this is not to say Sarah's world isnt great cause it clearly is. Sarah has written something i believe is rather unique. Which is a hard feat these days. Sarah's monster's are mainly human based with the assistant of demons. So just humans and demons, the reason why this world is so great is because the demons don't really do anything other than give people power - its the people who commit unspeakable crimes, all on their own free will, just because they crave ambition and power. This for me is truly a scary thought - I'll take monsters over terrible soulless cruel 'humans' anyday.
What the ba guy in this book does to his own son just for the chance of power.... *shudder* .... it's unimaginable - seriously, I have no clue how someone came up with this scheme. its devious, freakishly devious.

Speaking of the 'bad guy' there were heaps in this book! knock down one and another two take their place - this was good, kept things interesting.

I'm really glad I read this book, Thanks saraya for the rec and loan.

This is just the first book in a series but weirdly enough I don't feel the need to read the second one, I felt like everything was wrapped up rather nicely by the end. But i probs will anyways cause i enjoyed the ride.

Conclusion: Took me a while to get into it but the finish was quite satisfying. If you want something similar but different enough to the Cal Leandros series i would highly recommend The Demon's Lexicon - though the leandros series is much more adult in its brutality.

3.5 star rating for a good read.

Oh my. that was different. I can't believe he did that to his own kid! - I'm weirdly impressed.

I'm changing my theory a little. His parents did the deed while possessed. Though I still don't understand how Olivia hates Nick and not Black Arthur.

Alright I have a theory ready, Nick is half demon - which is why his mother always stares at him so.... horridly. Her life is some how tied into his - maybe if she dies he'll turn full demon or something. Which explains some of his more...violent nature and serious rage issues and probably why everyone seems to think he's a psychopath - He clearly has feelings there just... not as intense or easy for him to reach as everyone else, due to the whole demon thing.
I'm guessing his demon father? looks a lot like Nick, which might be why the female demon always seems to think he's someone else?
One problem, Alan is older so how was Nick conceived if the mother was no longer in the circle? 

hmmm.

either I've put my prejudice aside or this book is getting much more interesting I'm even starting to like the characters. Though the family still reminds me quite a bit of Nick, Cal and their mother. There's only a few differences. Mainly to do with the older brothers, Nick is way cooler. Plus he would always put his bro first. I am not sure if that's the case here or not. Suppose I'll have to wait and see. Either way I'm sure I'll still prefer the Leandros brothers, in the end, but I can always appreciate a good story.