I've heard nothing but good about this book since it came out (and unlike some people, Brett and his publisher had the sense to give away the first in the series even if it's older).
Brett has created a grim fantasy world. Every night, "demons" emerge from underground, determined to kill as many humans as possible. Victory is measured by the number of births relative to the number of deaths - and humanity is losing. The demons appear to prefer to hunt humans - and perhaps there's some explanation as to the origins of the conflict in the sequels.
Humanity's protection lies in magical wards, but the secret of constructing them (which appears to be mathematical) has been lost and as time passes, so have many of the wards themselves.
So, this is a story about, well, fighting back against impossible odds. It's also about rediscovery. Although it's not immediately obvious, this is also a post-apocalyptic story. It's definitely a fantasy, but I'm not entirely convinced it isn't a future Earth - again, maybe the sequels shed more light. Where did the "corelings" come from?
Oh, and it's also a story about courage and protecting what's yours. With some very well realized characters. It's every bit as good as rumor has it and I'll be tracking down the rest when I have a chance.
(Copy obtained at World Fantasy Con).