Irishman:
You bring up an interesting point. When the show first started, Meg was just an annoying teenage character. I think most people could identify with her teen issues: poor attempts at fitting in, trying to be popular (and failing miserably), being embarrassed by her family, wanting to get into college, etc.
But, as the show progresses, it seems that Meg has become an object of hate of the family. For the most part, I think this is for comedy's sake. We all have a family member we love but don't particularly like.
However, there have been Meg-centered episodes I don't care for. In particular, the episodes where she and Neil Goldman interact extensively. I also don't like the episode where she "fell in love" with Brian. The episode disturbed me so much, whenever it is repeated on Fox or Adult Swim, I switch channels.
Canonically (if that term could be applied to Family Guy), it could be explained by the fact that Meg isn't really Peter's child but is the result of an affair between Lois and someone else, as evidenced by Brian in an early episode.
It could also be explained by Peter's misogyny. On the surface, he cares more for his male family members and friends than the women in his life.
I do find Mila Kunis a more fitting voice for Meg, however. Lacey Chebert - as fine an actress as she is - didn't seem like a good vocal fit. Meg became more realistic to me after Mila Kunis took over the role.