Technically efficient, but not at it's place in the curve. Creatures with no other board impact than P/T at 6 mana don't accomplish much. If you're mulling yourself and simply Unearth him, then he's not a bad deal.
Slave Driver is AWESOME. In limited that is. Otherwise, he's merely ok. I wish he was a 3/3 for 5, that made a 3/3, and unearthed for 4. At 6 mana, he seems a little.. overcosted.
Oh well, still very cool in limited.
And. Why. Are. They. Reprinting... Hill Giant. W. T. F.
The Slavedriver is a very splashable 'bomb' to come from Conflux. At 4/4 it's large enough, and if it has to trade it still leaves you a smaller one. This guy is good enough to make the cut in my opinion, assuming you don't have enough bombs.
Grixis Slavedriver- A 4/4 for 5B is meh, but add to the ability to get a 2/2 zombie token when it dies and it becomes okay, add to that the ability to unearth for 3B and you've got a very solid card for limited.
Canyon Minotaur- This majorly sucks, a Hill Giant with different subtypes. Although given we've already had a Grizzly Bear equivilent in the block i'm not too surprised, limited playable.