This is way better than most people realize imo. If you're pressuring early enough, your opponent will never have time to waste 6 mana on 2 useless 3/3s, and if he removes it hes gonna have to deal with those 3/3s! The only other option is silence, but still leaves a 5/4 on the board.
No matter how you look at it, your opponent will always have to trade 2 for 1 to completely deal with this, always a lose-lose situation for them, this is VERY good. I can see this being played in aggro decks to top the curve, really cool design on this one!
Update: ok i forgot polymorph does deal with it 1 for 1, but who even runs polymorph effects these days? Doubt it will be widespread enough to make this card bad.