Maybe I take for granted that I know what Elves and Goblins are, while I suppose when he was writing that stuff, we had no frame of reference, so he had to do extra to create that world.
Granted, I only read the Hobbit, but even calling that a children's book is tough. I just feel like there's not a lot of actual story for the word-count. The parts where the characters actually did interact, I enjoyed. I thought that the Dwarf disagreement with Bilbo and the politics of the factions in the battle of the five armies was actually pretty good.
But listening to Bilbo opine over the miseries of a pitch black forest for 26 pages was pretty grueling.
LoTR isn't the same as the hobbit .. it's a much more expansive story