This is often worse than Doomsayer though because Doomsayer can often be played onto an empty board to force your opponent to pass the turn. In fact, except for mage with Frost Nova, that is often the whole point ofDoomsayer. This card wants to be played when you have lost the board but then your opponent can just go face with the minions that are corrupted and play new minions with no real tempo loss. I think this card will be worse than people think.
I dunno, but warlocks need a broadly playable spell for once. With PO getting banned, there is not a single warlock spell worth playing in most decks anymore. Warlock is the only class that has this problem and this card doesn't help with that. Warlock needs an identity - and spells are part of that.
The card itself is not very good either. It's too slow and not worth it to deal with aggro. Unlike Doomsayer, your opponent actually CAN PLAY CARDS on his turn - which is ALL the difference. Doomsayer, if it goes off, resets the board with your making the first move. That's not the case here. Might see play in heavy control decks, but I'm not even sure about that.
There's another downside - Doomsayer kills everything on the board at the start of your turn. Given the card text, it looks like any minions played by your opponent in the turn after you cast this would be unimpacted. Accordingly, your opponent can refill the board on his turn and will still have a tempo advantage over you.
This is a pretty decent card in the very early game if your opponent dumps his hand; but it will be relatively weaker as the game moves along and always weak against classes with access to cheap draw.