New Hearthstone cards are coming out, and the latest is a new Warlock card called Doom!
I, on the other hand, think this card is going to be a big deal.
Mostly I am of this opinion because of my suspicion that Warlocks are going to be playing C'thun decks when the expansion lands. C'thun, you may recall, looks like this, and has tons of cards that make it bigger when it finally does come out.
Imagine the choice: You can keep a small board and risk the enemy slamming down C'thun to clear that board and do a ton of face damage, or you can build a big board and get blown out by Doom! Both strategies are potentially disastrous, but because you don't know what the C'thun player is holding so you have to guess, and guessing wrong means you lose.
I completely agree that Doom! does not fit into current archetypes well. It is far too slow for aggressive Zoo Warlock decks, and the card draw and expense is problematic for Reno/Handlock decks. It might have a place in Combo Warlock (Leeroy/Power Overwhelming/Faceless) but even then it is 10 mana so it is a bit sketchy.
But we should not only look at old decks when we consider new cards. New decks mean new values, and an endgame spell that clears the board to help keep you alive, opens the door for C'thun lethal, and draws you into C'thun is just the ticket. You probably can't afford to run more than 1 just because 10 drops are really pricey, but it will be a hell of a thing when you do use it.
I predicted earlier that Warlock would get cards to make C'thun their default deck and this feels like it is part of that set of cards. It isn't enough on its own for sure, and Warlock definitely needs a specific card or two to make C'thun really effective, but Doom! is certainly a piece of the puzzle that will help C'thun Warlock being a real force in the upcoming meta, in standard in particular.