I thought this series was amazing, the last two episodes in particular, but the build up worked for me, I was petrified by the last episode, seeing the end coming.
What I found clever was that once caught, Paul had to face the gaze of other people. None of them saw him the same, the nurse saw him as a patient, with a bruised body, as a human, the psychiatrist saw him as a psychiatric patient, the nurse/carer in the ward stared at him a lot and perhaps saw him with disgust but also as an avenging angel, doing nothing to stop their sinister friendship growing, he also didn't resuscitate Paul at all, as was claimed on TV. The lawyer saw him as an income source.
Bit by bit, Paul started to see how others saw him, but it was when he was confronted with the truth- Stella told him he was an immature psychopath who needed to own what he'd done, and the psychiatrist told him that he would never be cured, both of whom he attacked for telling the truth, that Paul realised it was the end of the road for him. It was this blunt encounter with the truth that did for him in the end. There couldn't be an alternate realities (where he's humanized, where he gets therapy and gets better, where he stops his murderous impulses), so he jumps ship.
Stella looked worn out and shell-shocked, ok, perhaps the huskiness was overdone, but I think she was trying to show the emotional exhaustion of this process. Her boss (the drinker) the same. As someone else said, Paul's ripples of destruction were at their peak.
I loved it!