I binged it at the weekend, and was gripped. I agree that the way he was portrayed was not charismatic or attractive - he seemed to be wearing a bad wig, and appeared charmless, although as has been said, he must have been the opposite in real life.
I think the relationship between the main characters was a good portrayal of the way people get sucked in by psychopaths. They start by making you feel special and you get hooked on the feeling. Then they gradually withdraw their approval if you do anything to cross them, so you work harder and harder to make them happy. Meanwhile, you are slowly separated from friends and family, so the psychopath becomes your only source of support and contact, and in the end it is very difficult to get away, even if they have become abusive and you know that what they are doing is wrong. I thought Jenna Coleman played that very well, even though he was unconvincing.
I also liked the 'catch up' bits at the end, and hope that all the people caught up in catching him have managed to move on in some way. My heart goes out to the victims and their families, though.