I don't have a problem with it. It's not really good or bad. If it adds a lot to the original game, then I don't really mind picking it up for $10-15. If it's just reskins or small additions, I usually don't unless I have money left over I just want to get rid of.
They're quite entertaining to read. I've recently gotten into a few and have enjoyed them. As to why people say that, who knows. I think they're for anybody who wants to sit down and enjoy a good read. When it comes to kids, it's like most things, there are some that are age appropriate and some that aren't.