The article focuses primarily on difficulty levels and raiding. Watcher discusses in detail the problems inherent in the "10-man is easier, 25-man is harder" approach, as well as the ways that making 10- and 25-man raiding more equivalent in difficulty led to new problems that hadn't existed before. From there we learn about the origin of both the LFR and Flex raiding options from the perspective of how different raiding difficulties serve different portions of the WoW player population. If you've ever wondered about the thought processes that went into developing the different types of raid systems we see in the game today, this is an excellent article on exactly that.
Check out the full blue post after the break.