You can completely disable a Warlock and effectively remove him from the game if you just sit 1 person with an interrupt and a few stuns on him. Both in RBGs and Arena. I wouldn't mind seeing Destructions sustained damage buffed and Chaos Bolt damage nerfed (once chaos bolt is fixed and goes back to critting more than half your HP). Affliction are in a good spot right now, they bring Gateway which is fantastic and they can provide great dispel protection and spread damage (not spread pressure).
Overall, Warlocks are slightly undertuned at the moment, although it might be because of a couple of the stronger classes semi-counter Warlock.