This french show is a mix & match of other similar shows (Forever & Harrow come to mind).

Great premice, very good season 1 and 2.
Season 3 started to drop in quality (scenario).
Season 4's first episode is the end of the series, don't bother with the last two they pivoted in the worst possible way.

**Spoilers below**
[spoiler] In season 2, if you are used to the will they / won't they and whodunnit genre, you get pretty early that Maya might be the actual serial killer. Especially if you consider that this show was written [long] after The Mentalist. Furthermore, the fact that Balthazar gets back with her the night he was going to finaly have his date with Helene for no reason whatsoever after she left him when he was not feeling well in previous season is completely out of character.
Add to that the first episode of season 4 and you get that somewhere in season 3, some writers tried to create a twist thinking they were cleaver but ended up being unbelievably stupid and destroying the show's foundation. [/spoiler]