Series 1 and 2 of this show were fun and hugely enjoyable. The main characters were likable and the short episodes were bubbly and made you want to keep watching. A definite 5/5.
Series 3 was not as good, but still fun and enjoyable. I would say 3.5/5.
However, I am so sorry that series 4 was ever made and that I watched it. 0/5!
It was seriously bad, and, even worse, negated all of the positive feelings about the main female character. I ended up totally disliking her and the awful arc of the story.
Seriously, watch series 1 to 3 and skip series 4 entirely. The story line does not need series 4 and it ruins everything that came before.