Big fan of Spiral when I met up with some of my French cousins at our aunt's funeral a couple of years ago, during the course of conversations, I told them we were watching Spiral and they said they'd never heard of it, so maybe that's down to the explanation you give Witzend.
Another really good French series on a while back was "The Disappeared" which I see is on BBC IPlayer, I can certainly recommend that one for anyone who hasn't seen it.
I've heard "The Bureau" of Amazon Prime is good, but haven't seen that yet, annoyingly, doesn't seem to be included in their "Free to me" package.
Like others enjoyed some Scandi stuff, notably "The Bridge", "The Killing" and "Borgen" but after a while got some of their lacklustre stuff as well, not so "DNA" that's really good imo.