They're boring. I almost finished FotR. It was a chore. It's a great story, but it's not a thrilling narrative. The made up languages, poems, and songs certainly don't help either.
The films are far more accessible than the books. General audiences could watch them and enjoy them. And even if they don't enjoy them, they'd be crazy to not admit they're quality films with great effects, acting, scripting, directing, etc. I'll admit the story in the books is good and the history, languages, and lore are creative but I was bored to tears by it.... That's just me though!