Previously there were only two well-known Korean restaurants in Shadyside/Oakland/SQ Hill neighborhood: the Korean Garden and the Green Pepper. This Nak Won Garden is a new Korean restaurant, and my Korean classmates thought that it was the most authentic one.
So me and my gf went to the restaurant tonight, and ordered the salted fish, bibimbap, and the stir-fried pork belly. I thought the food was pretty authentic because I've been to a couple of cities in Korea. Also it wasn't too sweet or Americanized. The server (a Korean lady) was pretty nice and helpful, even though her English wasn't great.
In general I give it a 5, because of the food, service, and the location (close to Giant Eagle). I think it's really nice that Pittsburgh, as a city in the Mid-West, is getting more and more authentic Asian food.