The Simon R. Greene books are okay if you desperately need something to read, but don't expect anything uber fabulous as TDF.
The author has a great concept that draws from NeilG's Neverwhere, but the quality of writing is poor. The hints are too obvious, key events happen too soon with too little character development. And there are a few other minor things that bother me. (Like how their magic lacks rules and constraints) I'm only up to book 5 : Path's Not Taken. But if you read the first book, it is a pretty good indicator for how the rest of the series is going to be. So pick up the first one, give it a read. Your milage may vary.
If your attention span is lacking, or if you just want a quick, simple, easy to follow urban fantasy read, I would give them a shot.
I personally dislike the selfless approach the authors of older books take.
“I do not love the bright sword for it's sharpness, nor the arrow for it's swiftness, nor the warrior for his glory. I love only that which they defend”
With me it's the other way around, I'm sick and tired of slave like characters in popular media and sadly so many fiction books that care for inept individuals or fight for their gods and their glory instead of gaining something from their lack of strength and wits or fight for any other egoistical sake. That's my take on the vast majority of fantasy literature and why it doesn't crank my well.
But even if one day I'll read a book about a character that lives up to my objectivist values it's still gonna be just a book, a time killer. And meh, I aint goona read fantasy books written by women, I'm a sexist too, besides I'm sure I'll drop Spirit Thief at some point.