2 damage for 1 quanta is pretty darned cheap, and I could well see this replacing shockwave in some decks. I do agree thunderstorm needed some sort of change, though, since it was one of the least used cards in the game. It could probably stand to have a cost increase, now, though, if we stick with the 2 damage thing. With rain of fire/firestorm at 7 // 5, and fire being more efficient at damage dealing, a 2 damage version should cost slightly more than 2/3 of that, so maybe something like 5 // 4, or 4 // 3?
Earlier, I'd been thinking it would be cool if thunderstorm did something like bonus damage to airborne creatures or water creatures or something like that; maybe it could do 1 damage to all opposing creatures, then +1 to airborne ones and/or +1 again to water ones, depending where Zanz wanted to take the card.