I've enjoyed the fantasy novels by Glen Cook about a p.i. named Garrett, so Dragon Precinct seemed like it might be fun. It's more or less an attempt to come up with the fantasy novel equivalent of an 87th Precinct novel. Too bad it didn't work very well.
My problems with the book included characters that I didn't find very interesting, threads that didn't really develop, and an ending that comes from way out in left field (it's a variation on what Roger Ebert calls the "idiot plot," and it relies on someone's not giving essential information at the beginning of the investigation, information that would have rendered the rest of the book unnecessary).
What did I like? Well, the book concentrates on the procedural details instead of the magic angle, and the world-building isn't bad. All in all, though, the book wasn't strong enough to make me want to read another one in the series, assuming that one was ever published. DeCandido has written a ton of media tie-ins (Buffy, Star Trek, Farscape, Serenity, etc.), and this seems to have been an attempt to establish his own territory. Maybe it would work better for you than it did for me.