I've watched it all now.
I didn't find it funny as such - I found myself cringing rather than laughing. A bit like The Office - observational rather than laugh-out-loud.
Having said that, I think most of the characters are pretty vile. The old woman is awful, with no redeeming features. Kelly is awful with no self-awareness whatsoever.
The son is selfish and immature. Pauline is particularly awful, particularly to Derek.
What I really don't get is why Cathy puts up with them all, and why she doesn't appear to have any sort of life outside of the family.
The best character is Derek imho- he is a bit more sympathetic and you kind of root for him, even though he's so pathetic and needy.
It's compulsive viewing though. .