To say that The Demon's Lexicon blew me away would be quite the understatement.
I think the most crucial element of The Demon's Lexicon is its ending. It gives sense to the complete book ' its characters, the storylines, everything takes sense in the last few chapters. I know some people thought the beginning was a little slow. My advice : if you do but still enjoy the writing and the story, don't despair! The ending really makes it worth it.
Personally though, I didn't find it slow. I started reading it one night, as I was going to bed, and I was drawn in from the first line. I had a hard time putting it down and going to sleep! The story was on my mind for many days after. It's made my mind whirl and twirl, and after finishing it I would definitely re-read it with a new perspective.
The characters were wonderfully written, and I had a clear picture of who they were. At first, they did look a little uni-dimensional (Nick the troublemaker, Alan the wise protector, etc), but as the story progressed I could see how much more there was to them. Nick is the one we follow around, and he definitely makes a captivating main character. That's not to say his brother, Alan, or the two other siblings who join them, Jamie and Mae, aren't interesting. Jamie's sarcasm was particularly enjoyable.
Now, what to say about the world the author created? Mysterious, dark, and a little disturbing, it is our world filled with mystical beings who, mostly, have no good on their minds. My first thought was Supernatural meets Buffy meets something else that makes it unique. It really was different from the usual vampire or werewolf urban fantasy, and it's also a book that I wouldn't hesitate recommending to both guys and girls.