Started watching from series 3, fortunately series 1 and 2 were on catchup,eagerly waiting for series 6. How anybody cannot be hooked on this drama is beyond me, anyone I have recommened Line of duty to has said the same thing 'I need to watch the other series I've missed' or ' It's one of the best dramas I've ever seen'.
I've not seen any of Jed Mercurios' other dramas except Bodyguard which was another briliantly written drama, his storylines are so well crafted to not only include clever plot twists but also the politics of high ranking police officers and the flaws of the main characters.
With the amount of reality show dross that is churned out on a weekly basis dramas like Line of Duty are ten times more believable.
As for the realism of the show, without the odd act of violence and swear word then it would not be realistic, would it!