Arhar's moment of glory in the sun...
Personally, I'm starting to come off my 'high' as far as this card is concerned. I thought it was damn near broken, and fairly insistant that the '1' in the upper right hand corner was really a '4.' Then it would be overcosted, and therefore the work of WotC. Woo-hoo! On reconsidering this, I've concluded that the card is _slightly_ better than Vendetta, but isn't the same type of card, i.e., the two should not be replacing each other, at least not in my decks.
I think Do or Die compares more admirably to Wrath of God, punishing your opponent for overextending to get past your defenses. A series of blockers that won't die in combat forces your opponent to play out more creatures over a couple turns to work past you, letting Do or Die take over as one of the best removal spells you can get at that casting cost. In order for it to be good, you need to force overextension, and that's best done on the defensive; you play blockers so your opponent must go _past_ you with more creatures.
Vendetta, on the other hand, fits aggressive decks. You play down _your_ attack force, and your opponent must drop blockers. You blow up a blocker, and bust through for a kill. While the aspect of overextension is similar, you, as the aggressive player, usually don't want to overextend yourself (or else Do or Die wrecks YOU). Thus, you play only one or two fast critters, and make your opponent deal. Chances are, your opponent drops two blockers, leaving you to Vendetta one and bust through.
Of course, this comparasion is based off the theory of aggro vs. control, and one the idea that, when actually playing, games where Vendetta is actually played against Do or Die would be rare.
But, on general princibles, the two are in direct opposition. One, like Wrath, clears the board and punishes overextension, gaining card advantage in a control deck. The other takes out blockers while keeping _you_ from needing to overextend, letting you bust through the last few damage...
Am I screwy 'cause it's 7:00 AM? Or am I making something vaguely resembling sense?