I'd agree about Lois, but it becomes way too distracting to have slowly seen her become a slutty mom. The earlier seasons always alluded to the idea that she was "loose" back in her youth (KISS and 'Loose Lois') but it had become pretty well known that she had sewed up her wild youth and settled down to be a mother. Since the revival though, it seems they are trying too hard to make her some sort of sex pot. The episode where she cheated on Peter with Clinton digressed her character a lot even though Peter slept with Clinton in the end for a throwaway joke, the damage had been done to her character.
I've heard the argument from people saying "Peter treats her horribly or acts horribly so it's okay" but if you remember in the original seasons, Peter never would have hurt Lois in any intentional way, neither of them would ever have committed adultery either. Lois also has become very cruel to her children in recent seasons, earlier on in the series run she usually was the sole defendent of Meg, now she mocks her with the rest of them.
I guess that's the direction they wanted to take her character, and you know what that's totally fine but for any viewer, there's an incredible shift in tone between about season 4 through the present for her character that can't go without notice.