Hour of Devastation. And while there are several interesting Commons that have already been spoiled, the existence of a cycle of Common Lands that can be cycled will probably make a big difference in the upcoming metagame. One of the perennial problems in Magic is drawing too many Lands in the course of a game. Lands that cycle solve this problem quite elegantly, allowing you to discard them for a new card and a marginal cost. Unless you're playing a very aggressive deck where the fact that these Lands come into play tapped is an issue or need a very finely tuned mana base, including a full playset of these in your deck is probably a good idea.
In this case, the cost to draw the new cards is 2 mana, one of which (presumably) is the same color as the land would have produced. This is somewhat of a blend of the original cycle back in Urza's Saga (which has never been available on Magic Online) that cycled for 2 mana and the newer one from Onslaught that cycled for a single colored mana.
Interestingly enough, it appears that each land in the cycle will also be a Desert, which looks like it will matter for at least a few cards at Common.
Finally, I want to apologize for the lack of content. June has been extremely busy. I haven't had time to open Magic Online in weeks, and all of my other hobbies are suffering as well. The rest of the summer looks quieter fortunately, so I should be back to a more regular schedule from this point forward.