Now I've seen the first 2 series I think that shortly into Season 2 the writers got lost in the plot lines.
The really interesting part for me in Series 1 was how Villanelle planned and carried out her murders in such a cold but almost humorous way, it was really intriguing. The chase or hunt for her developed into a great series but once the relationships became the whole plot, the writers seem to have got lost in what the point was, it was a mash of characters simply dropping in & out (or getting killed off) and the chase became a mess of mixed relationships and double meanings, while others saw the bisexual link between the main characters as unique, I found it a bit overdone and frustrating.
In all it was an unusual show that started really well (S1) and got lost in itself.