Out of curiosity, which matchups does Kazakus help you in as a Warlock?
It was great in all tempo matchups. Playing like 2x 5/5 with taunt, divine shield, lifesteal or stealth was huge, too much for Paladin, Hunter or Warrior to just ignire and go face. You could also have poison + damage (for instant mass removal), lifesteal + damage (for instant heal), freeze (for stale), buff for your other minions (great with taunts on board), spell damage (awesome with removals) or even card draw. Just an overall outstanding card.
Definitely a great card. I just question whether it's really needed in those matchups. You're not using it to pressure; you're using it to heal, remove, or force trades generally. There are other cards than can serve a similar function. And with the Crabrider nerf, I think you'll generally have an easier time removing early on and have less trouble stabilizing late game.