In an aggro meta this is such a great card. Against control, not so much. Quite frankly, it's very well designed - it's a tech choice that's fantastic when chosen appropriately, and pretty darn underwhelming when not (think cards like The Black Knight and Harrison Jones - great when they hit their mark, below average otherwise).
I totally misread this card. I thought your hero would lose health, not the minion. Sucks.
I disagree. I think it is an insanely good card, and if it took away from your health instead it would be unplayable in a few classes. Maybe one of the best card in the entire set in my opinion. It is a game-saver against many aggressive and tempo decks, and while it is pretty bad against Warlock or combo decks, you generally don't need strong taunts against most of them anyway.