Warlords of Draenor is bringing some very significant changes that will greatly simplify the unecessary complexity of each class and specializations.
The Great Squish
Don't be too alarmed by the item level squish. Almost all of the changes will quickly become imperceptable due to the fact that health pools are being brought down alongside the item levels. Another important part of this change is the removal of flat based damage/health/resource numbers in favor of percentage based effects on those respective point pools.
Not too surprisingly, Blizzard has chosen to finally revamp all of the racial abilities and passives with the exception of two recent races: Worgen and Pandaren. All of the Hit/Expertise based passives (such as weapon specializations) are being removed or replaced by secondary stat buffs that are appropriately themed for each race as needed. The few racial abilities that were way too strong by comparison are being riegned in and the rest are being brought up to par to level the playing field. Blizzard has expressed that they do want your choice of race to matter in small ways, but not so much that you feel like you made the "wrong" choice by playing your favorite race.
Read more on racial ability changes here.
Up to 20% of abilities are being eliminated or consolidated per class and specialization. A fair amount of core class abilities are being removed from use by multiple specilizations, in favor of one specialization in each class. Cooldowns, particularly of the DPS variety, are being consolidated to reduce the amount of stacking during combat. Crowd control as we know it is going away. Many abilities are being changed to be easier to escape, last shorter amounts of time or completely removed altogether (farewell Disarm).
Check out the full Dev Watercooler.