I think this is true. I read the first two books, but only saw the first movie. They left out so many important things, it lost so much. I can see where someone that hadn't read them would be lost.
The second book I could barely finish, so I quit after that one, and never saw the other films. I haven't heard good things about them.
If they have to recast to air the final film on TV, that is just pointless and they should just leave it alone.