I have to agree with you- the Dursleys are terrible people! It's also sort of a challenge to myself, and something I really wanted to do. There are lots of stories that feature physically abusive Dursleys, and some stories do it very well. What I wanted to see more is emotional and verbal abuse. They're just as harmful as physical abuse, and perhaps even more dangerous because there aren't any outward signs like bruises, so it's easily missed. 

It's a very personal topic to me, and I'm glad to see that the interactions between Dursleys and Harry are well-recieved.