This Korean restaurant is a great place to go if you are not familiar with Korean food or live too far from the "Korea Town" area near I-35.
For Korean food, I would definitely suggest the Kal Bi (prime short ribs) or the Bul Go Gi (shredded ribeye steak). A great appetizer is the Chap Chae, which is stir-fried glass noodles with veggies.
The sushi is great. The nigiri (2-piece per order raw fish) is fresh, and the rolls are innovative and interesting. I suggest the Mt. Fuji roll, which has really delicious shredded crab on the outside, the Naan Special, and the usuals Caterpillar Roll, Volcano Roll, and Shrimp Tempura. Also ask them what they have on special -- they sometimes have rolls that the sushi chefs are trying out, which are also delicious.
The atmosphere is really classy and there is even a bar for after-hours. As far as the crowd, I usually see a mix of all types of people in the restaurant. The bar side usually has a late-20s to late-30s "sophisticated" crowd hanging out. I think Naan is really the best bar to go to near the Legacy/Tollway area, and definitely the best sushi outside of downtown.
FYI, their real website is www.naanrestaurant.com, not the website above.