Honestly, this isn't a terrible card. Sure, it can only hit one creature, but what were you expecting, a black Fireball? Granted, WotC made a slightly better version of this card in the form of Sorin's Thrist, but that card can't be scaled to suit the needs of the caster like this one can. The double-black startup cost can be a hinderance, especially if you have 8 mana and need to kill that Elderscale Wurm in order to win. Also, the speed of this card is also kind of a restriction since you'll have to dump your mana into it on your turn, making it hard to play nice things and this card. Still, not a bad option if you're looking for a scaleable Sorin's Thirst.
Pros: Scaleable to your needs
Cons: Sorcery-speed, double-black startup