I'm looking at his numbers on the LoL Wikia and it looks like he's a bit OP.
His base stats are on the high side and make him a bit more durable than one would expect and assassin type champ. Plus, his Razor Shuriken has a base damage of 75 without including the shadows. His CC is incredibly good, especially if you can get his clone to attack as well. Being able to swap places gives him nice mobility and his ultimate, which makes him untargetable, might actually be able to be used aggressively in order to dodge an incoming ultimate and launch a counter attack of your own.
He looks like tons of fun and a definite challenge to use, so I'm still going to buy him once I've got enough IP. I hope other people will insta-buy him and let us know if he is truly OP or not because I'm just speculating here.