As you can see, some works which are famous for being impenetrable get their reputation from their complexity and not their length. James Joyces's Ulysses, for example, is far shorter at 262 thousand words than Gone with the Wind, and yet I was able to finish the latter and not the former.
At 808 thousand words, the Harry Potter series is far longer than Lord of the Rings and yet I found the former to be a much more enjoyable read (I still haven't finished LotR). On the other hand, both are positively dwarfed by the Game of Throne series, which has already reached 1.77 million words and is still growing. Now that was a frankly tedious read which I only managed to finish out of a sense of masochism.
Which book did you find impenetrable?