Regardless of what you think of WoW, the regular game design blogs by Ghostcrawler are generally worth reading. The latest one is very worth reading. Not for the topic itself, which might go a bit too much into specifics if you don't play WoW (anymore). But for the general approach.
You can watch live how the class designers try to keep the players' minds busy without asking them to do something frustrating.
Don't read the comments unless you already lost your faith in humanity.