Yarb, I don't feel any of the books were a let down. A book to me was never a marathon but casual reading. That said, I had no issues with any of Jordan's books. The story he created is so AWESOME I wouldn't care if a 5th grader wrote it. The sheer amount of side stories all being tracked at once is staggering, and it all comes together towards the end.
When I see someone tell me they got bored in the middle, sounds like to me they were in a marathon rather than casual. All stories do it, the middle did just fine in my opinion.
That said, I ALWAYS had difficulty putting the wheel of time books down...just one more page, chapter, etc