A shitty EDH knockoff that SCG is pushing hard so they can jack up the price of so-called "staples."
I think that's an unfair characterization. I thought it sounded dumb at first too, but it has some compelling features.
The rules are that you still have a Commander with the same color restrictions, but your deck must be 50 cards and nothing in the deck can have a converted mana cost greater than three. You start with 25 life, and the banned list is designed around one-on-one play.
What this means is that the decks are much easier to assemble, the games are easier to organize, the games are much faster and to the point, and stupid combos are both rarer (because of the cmc restriction) and easier to disrupt (because discard and counterspells are actually good in 1v1).
Another bonus is that suddenly some cards that would otherwise be useless now become very relevant. Black Sun's Zenith, Gaze of Granite, and Forced March, for example, are all-stars because they're some of the only Wrath effects that are legal in the format.
I'm trying to put together a Pharika deck right now, designed around wrathing the board repeatedly while playing threats that either don't die or can be recurred indefinitely.