Same old same old.
Every expansion gets this complaint. For one, not everyone is a progression raider. To release more content before people are far enough along would discount the point of the earlier content to an extent, especially thanks to raid finder.
Two, you can't possibly have experienced everything WoD has to offer. Aside from raiding, there are a multitude of quests, PvP, scenarios and achievements to name a few. The game is full of content, you just have to be willing to get into it.
This is such a bogus, whiney argument that is typically reserved for the main forum trolls. It is difficult to balance content release with a game so varied as WoW. But, what is a WoW gamer if they are not complaining?