I watched this when it originally aired but never finished it. And I couldn´t remember why. So I decided to re-watch and it came back why I quit.
That Jack plot already became very boring somewhere in the middle of the second season, it just wasn´t going anywhere. And catching him was to easy a task in the end if you consider what kind of complexity they wrote into the character in the first place. It didn´t help that the actor playing Jack in the third was different from the one who did it the first two years. The first Jack was a genius, obsessed maniac. The one we finally see is a sad excuse of that and reminds me more a poor mans Dr. Lecter. (Suplement: After further watching I should withdraw that part of the comment, it is premature - if you´ve watched you know why. This may explain some things but it didn´t helped the show from where I stand because now all of a sudden it seems "Jack" has been a group of people.)
Than there is Dr. Waters - the know-it-all. Everytime someone is making a suggestion on a case, with here it´s always "No, that´s not it" and then comes the lecture-like explanation why they are wrong. I never felt any sympathy for her and her situation as I never felt drawn to any character of the show.
They also tried a lot of different sub-plots in the second season f.e. Baileys daughter or his relationship with the ex-wife of a colleague (or his own ex for that matter) but they too went nowhere because they were either closed out to fast or never really developed further.
The other characters in the show never got much of a background so they appear unintertesting. I´m writing this while I´m a quarter into the third and maybe some of the things mentioned above will change. I will go through the end this time but for me this is at best an average crime show. I´ve already had a couple of episodes that couldn´t grap my attention and just played in the back.

After the conclusion of the Jack-plot I decided not to go along with the show any longer. There just isn´t anything in it that interests me.