Now that I'm up-to-speed on this series, when I look at the publication date of this latest novel (2009) and don't see definite plans for another novel in the works, my feelings can probably be best expressed in lolcat: MIKE CAREY, WHY U NO RITE MOAR FELIX??
But in all seriousness, I really feel like this series stands out from the other cookie-cutter urban fantasy novels, mostly because of Felix. In the scale of urban fantasy heroes and antiheroes, he falls somewhere right in between the blazing righteousness of Harry Dresden and the sometimes gleeful bloodlust of Cal Leandros. He manages to save the day, but not without a few screw-ups and morally-gray decisions along the way. And he knows who (and what) he is.
I also find the world quite intriguing, and I like that Carey chose to focus on ghosts and demons rather than throwing other sorts of supernatural creatures into the mix. He has an interesting take on werewolves and zombies, and it almost seems a shame to stop the creative engine here right when the world seemed poised on the cusp of a great change.
And yet, if Carey never wrote another Felix novel, I'm pretty satisfied with the way things ended now. One of the major arcs of the story has come to a conclusion, and while I felt some things didn't get resolved, there are easily quite a few threads Carey could pick up again if he does continue with the series.