As far as police dramas go, this one sets itself apart in many ways, but primarily in how damaged the main character is. Ian does a terrific job as Jack, but he makes it very difficult to root for at times; which is ok once or twice in a show like this, but not as often as here IMHO.
The writing was overall quite good and gritty, however the chemistry between the characters took a nose-dive when Noonan was replaced by another actress. Not sure why the change occurred, and they all did as well as they could with what they were given, but between the lack of internal development with Jack and the unfortunate casting change without adjusting the role as to create a better segue, it's not too surprising how short lived the show ended up being.
Having said that, the characters were interesting, for the most part, and the plots were unique-enough to carry each episode on its own. The entire show could be comfortably watched over a weekend.