This series should be marked under the "not bad but could have been so much better" category.
In terms of the positives. The editing is quite good and the pace is kept up quite well. The score does a very good job of raising the tension at the appropriate moments. The cinematography is high quality and the series overall was very well shot.
Now to the less than positive points. First off the premise is not very original and in the end very contrived. Its as if someone took the plotlines of Silence of the Lambs (using an imprisoned serial killer to catch their admirer), Seven (a serial killer who ritually tortures their victims as punishment) and Copycat (a serial killer imitating the crimes of a convicted murderer).
Secondly, the characters are all pretty one dimensional and the acting is actually quite flat. Carole Bouquet is as cold and distant as ever, meaning it is difficult to feel anything for her, positively or negatively. Fred Testot, who plays her son, mopes around and seems pointedly uninteresting as a character. Its hard to see from this what his wife saw in him. The other characters are pretty much stereotypes (the grizzled police chief, the disgruntled/resentful partner who was passed over for promotion, the deranged serial killer, etc).
Lastly some of the plot lines stretch credibility a bit too far. For example, France's most notorious serial killer is left with only one guard. The police decide race to rescue the serial killer' victims by racing across Paris only to arrive too late instead of calling for local backup.
All in all, with a bit more originality in the scenario and a tighter script, this could have been excellent.
