I haven't even read the book, but from the little I know there has been significant divergence from the source material.
I'm a little tired of random people that we've never seen - who apparently the residents of this small town where everyone knows everyone have also never met or known about - showing up so long after the dome came down. The Agatha thing - how is it even possible that she was living there and Big Jim never knew she was there? He has his nose in EVERYBODY's business! And it is completely unrealistic that Maxine and Agatha would have laid low when the dome came down instead of searching out other people. I mean, compared to the dome thing happening at all, which is of course totally believable