Instant-speed boardwipes are pretty rare and this is one of the best (topped only by Evacuation in my opinion). This card is great for two reasons. First is its speed, which is, as I've mentioned, amazing. Second is its Cycling. If you've got this in your hand but have no reason to use it, you can easily get rid of it in exchange for another card (again, at Instant-speed). The only issue I have with it is that it's an x-cost spell, so you may not have enough mana to deal with the problems to need too. That, and it deals damage instead of straight-up killing, but that's more a red issue rather than specific to this card.
Pros: Instant-speed boardwipe, usable even if not castable