Things I liked: The whole freaking book.
Things I didn't like: Finishing, realizing that there will never be another WoT book for me to look forward to.
But isn't the DO described as a huge force in the universe? He's not really a being - he is described as evil itself, or the manifestation of all evil. Destroying him is akin to destroying evil in its totality. At least that's how I read the passages where Rand really got to know the DO.