Hearthpwn

Does Blingtron destroy a weapon or just replace it?

Doom is a tech card, in the way that it will be used depending on what the current meta is.  Doom is not a bad card, it's just one that a specific usage.  Deathwing also has a specific usage too, but that is very different.

The most important thing to note is Doom is an anti control card.  You want to use this in a control heavy meta.
The decks Doom is useful in are Midrange and the slower zoo decks.  You have to survive to 10 mana firstly.  Secondly you need to win soon after playing Doom to avoid fatigue.

How this card works is like this:  You play your Midrange or slower Zoo deck.  You hit T10 or later in the game, you are out of steam, used most or all of your hand and the hero power will not give you enough draw to get you back into the game.  At this point you really hope your end game control opponent goes all in, overextends himself so he can win on the next turn.  He does not win on the next turn cause you used Doom.
Why this is important that he over extends himself, is most control decks by the end don't have much draw.  You need to ensure he does not have much of a hand at all to play on his turn directly after you play Doom.  Him overextending himself is the perfect time to achieve this.  You want his turn right after your Doom to be as weak as possible.  Then on your turn you can use all the draw Doom gave you to remove what he put on the board that turn and fill your side of the board.

Vs less skilled control players, Doom is potentially a great card.  Vs more skilled control players, they will know Doom is a possibility and will not ever overextend themselves end game because they can be Doomed.  This does work in the Warlock's favour as you know you'll never have a massive enemy board to deal with.

Control decks can get a little use out of Doom, but only if they use it as a bluff.  By that I mean if enough control locks run Doom, then no one else vsing them will extend their board end game.  This makes control locks life easier.  This means in theory you don't even have to have Doom in your deck for the effect, but you do need the threat of Doom being present in control lock decks.  Honestly, this possibility I do not think will happen. I do think Doom will be more used by midrange and slower zoo decks end game to punish control decks that over extend themselves.

The key to using Doom successfully, is to manage the initial tempo loss.  You need their follow up turn to be as weak as possible.  Achieve this (it's situationally achievable only) then you open up the can of whoop ass on your next turn.