What he got wrong is that they're perfectly fun and good films in their own right - it'd be more accurate to say they're heavily inspired by the LoTR books rather than being direct adaptions. In some cases they cut things which just would never have even worked on screen, and in general I don't think a deeply ponderous and weighty mood would have really been received that well. That said, some of the changes they made (e.g. to Denethor) were just gratuitous.