After reading other people's reviews, good and bad, I decided to watch the entire series anyway. Overall, I thought it was a terrific, and yes, dark themed show.
I've only really known Stana Katic from the Castle series, which I loved, despite the differences she and Nathan Fillion had.
I thought the build up of the story/mystery surrounding who the ultimate "bad guys" were was great. Yes, some of the storyline was over the top, but this is TV we're talking about, not real life.
The acting overall was good, some actors better than others, but you have to put the acting in perspective with the type of show. This is not Academy Award material, but I wanted entertainment, and got just that.
Season 3, in my opinion was awesome, and I don't want to say too much, hence a spoiler alert.
Now to the ending...I hate stupid endings in a series that I've become find of, and this one did not disappoint.
If you want a drama/crime show with pure entertainment, this is your show!!!