The Lord of the Rings by J.R.R. Tolkien is a great book and a nerd's delight, but the first two books of it--which comprise Fellowship--really are a sequel that shouldn't have worked. A short children's fantasy gets followed by a thousand pages that essentially retcons your memories and makes them something else.

As a sequel to The Hobbit, Fellowship is a mess. Fortunately, it was so much more than just a sequel. 

Tolkien, J.R.R. The Fellowship of the Ring. London: Harper Collins. 2010.