Well, I really like this card; I'll certainly be using this, particularly in certain types of decks. It could be used in conjunction with things like malignant cell and bone wall, for instance, or, more practically, with shards of focus once you've used them at least once to get an extra use out of them. (or to kill enemy focus before they get a chance to use it!) Comparing to thunderstorm, it's definitely more powerful, but things across elements aren't always equal, such as horned frog vs blue crawler, so that's not necessarily a bad thing. Thunderstorm could always in theory be buffed as well, with something like -1 cost or doing extra damage to water creatures, or airborne creatures, or something like that, if needed.
Edit: Also, I want to add that I'm a big fan of cards where the upped version isn't always strictly better than the unupped. (obvious ones like chaos seed and toadfish, but also the ones less so such as pandemonium, rage potion, mind flayer, phoenix, etc)