This card and I have a little history together. During a debate about Infect online, I was talking about how cards like Skithiryx, the Blight Dragon can't even behind the "doesn't die to Doom Blade" argument for balance. This guy's response? "No one uses Doom Blade anymore! It sucks! Vendetta is so much better!" Now, this argument is flawed for 2 reasons. First, Doom Blade, does in fact, not suck. It is still one of the most powerful kill spells in Magic. Second, and more importantly, this card isn't really that good. Seriously.
Let's look at the good things about this card first. Almost universal kill spell for 1? Sounds pretty awesome, especially since it's at instant speed. However, the speed of the card is counter-acted with the downfall of the life loss. I've seen the following sequence of play, or something like it happen more than once:
Player 1: "I swing with my Terra Stomper"
Player 2: "I hit it with Vendetta"
Player 1: "In response, I Strength of the Tajuru for 8, making Terra Stomper a 16/16. You lose."
Player 2: "Crap..."
This card is, more often than not, going to backfire. Early game, it might be worth the gamble, but later on in the game, the risk usually outweighs the benefits.
Pros: Cheap, quick kill spell
Cons: The life loss can easily be turned against you