I cannot praise this show enough. I agree with other reviewers on the high bar this show sets for the genre. It is the French Homeland, but more credible, low-keyed and deeper.
Everything distills quality here: a really, really superb script which is intelligent, sensible and gripping to the end; extraordinary characterisation and performances from the main to the last character; tremendous production and attention to detail; credible information about the metier; an impeccable direction which keeps extreme suspense and intrigue, only without the flamboyant, explosive special effects so inevitable in American series, but it is still very action- and field-oriented.
Season 4 is really fantastic, it has not decayed in the least. The addition of Mathieu Amalric makes an extra bonus, with the talent he brings to fore in every performance. Marie-Jeanne acquires more weight in the show in the most positive sense. Florence Loiret Caille is such a superb, nuanced actress! And the priceless Kassowits recreates his complex Malotru, the antihero always full of surprises which you respect, admire and love as the seasons go by. He is the perfect spinal cord for the show.
In short, this is the most exciting show in the year. I really hope it will maintain the high quality and the cast in years to come, to the delight of all the genre lovers. Kudos to everyone involved in the production!