Green doesn't like flying creatures, does it? This is a pretty decent card, even though it only hits flying creatures. For green, it's a decent card because it does a good chunk of damage to flying creatures, which green tends to have a little bit of an issue with (although it has cards like Wing Snare). The fact that it does 4 damage means it'll probably kill creatures up into the mid-game (probably up to turn 5). It's also well-costed (Pyroclasm costs 2 for 2 damage). All-in-all, it's a decent card.
Pros: Mass 4 damage for 3 mana
Cons: Only hits flying creatures, sorcery speed