Honestly it looks pretty good. It's a 5/8 Eldrazi for only 6 mana. Also when it enters play, you exile the top 4 cards of a target opponent's deck. After that you get to play any number of land cards that player has in exile.
What I particularly like about this guy is not only is he pretty cheap mana curve wise but those lands you get to choose from are not limited to those exiled by his effect. Has your opponent Delved away fetch lands? You get to grab them! Remove an opponent's graveyard to exile? You can shop for as many lands as you like.
If this playing cards from exile thing becomes a theme of this new set, Battle for Zendikar could have some terribly powerful cards. The sower will probably be even better in eternal formats where lands can hit the graveyard regularly, especially legacy. This is some crazy free mana ramp,and it only has to hit two on a regular basis. This is not a card I'd like to play against. Plus this mill into exile effect probably isn't alone in the set. This is pretty good stuff.