Don't take it personally, Masterfurry. It's all about the card.
While the ability to smash my opponent's hand brings joy to my heart, the ability for my opponent to smash my hand and give me cards that do not match my towers does not.
Nightmare restricts the ability of the player for a turn, along with putting a crimp on extra draws. This, however, would wipe out a strategy completely -- a total game killer for the player hit. Consider how many times you've sat with a card in your hand for 15 rounds waiting to use it (like, that random Photon to go with your Eternity to keep from decking out).
My worry isn't so much that a player using this card would win every game, but that its use (up to 6 times per round) would be frustrating enough to drive many players away from PvP. Please consider severely limiting its power -- perhaps to duplicating cards from your opponents deck until your hand is filled, or perhaps swapping a couple of cards (tops).