Line of Duty

So that's it, done and dusted, series 3 of Line of Duty comes to an end. Already, they know there'll be a series 4, and yes, I suppose I'll watch it, but each time the mixture gets diluted. The core of it, the interrogation stuff, is still terrific, but there's too much else that isn't convincing. Kate going undercover, Craig Parkinson doing his crook cop act again (why did we have to know from the start what he was doing?), and the whole simplified, over-personal storyline around the Polly Walker character - none of this was really worthy of Line of Duty as we've known it in the first two series.  Daniel Mays was wasted before he began, which is why they had to bring Lindsay Denton back, and lean so heavily on series 2. Yes, it's been great, but i'm not sure it needs to be kept going for ever, not if this series is anything to go by. Why do they always have to recycle stuff, beyond its sell-by date?