I watched series 3 right through to the end, but to be honest wish I hadn't bothered. Too convoluted , too many holes, and just plain silly really. I could go on and on about the weaknesses. How many people in that police team? How many people working the 18 hour day solving the crime? Oh just 2. And how come every suspect, and there were many many many of them, were all still working till 10 or 11 in evening in their garage or shop etc. when the police went to interview them. And re interviews, don't the writers know that suspects under arrest usually have a Duty Solicitor at the least? Forensic results within 20 mins by the look of it too. That's a bit unusual. ;)
Probably didn't help that I'd just binge watched all 5 series of Line of Duty, which was strong, clear, shocking, surprising and clever right to the end.
OK some very strong performances from Coleman, Tennant and Jodie Whittaker but in a word, you won't miss much if you stop at series 2.