So in this world there are 'wardens', who are basically a bureaucracy of magicians with control over water/fire/earth/air operating for the 'greater good' and preventing natural disaster, supported by slave-like djinns and attacked on occasion by malignant demons. This world is reasonably well set-up and hangs together for the duration of the story well-enough to keep you engaged.
Where it starts to come apart is with the stereotypically feisty yet irresistible yet uber-talented heroine. She starts off quite well (compared to some others in this genre) but soon descends into ludicrously irrational acts - for example: falling in love at the drop of a hat (despite her oh-so cynical personality), at the height of trying to save those she loves from slavery/certain death she gets all excited about a new car, when offered a really obvious and easy choice for preventing the one she loves being attacked she refuses to on a point of principle (or is it to stretch the story out - you decide!)
I'm starting to lose faith in this urban-fantasy malarkey - I like the ideas, but the characterisation is so diabolical and the ploys so contrived and hackneyed that I think I might have to give up the ghost. The early Anita Blake books (before they turned into porn) are the best examples I have come across, everything else has disappointed.