Dana DC
Google
Compared to Myeongdong, here are fewer tourists, very short lines and it has a laid back, modern atmosphere which makes it a pleasure to shop. It is is spread on 2 floors, first one with mainly luxury goods and second one with korean cosmetics. You can try them before buying which is convenient.
However I had some problems managing to get to that place from Jamsil station up to 8 -9th floor. It was rather confusing even if I visited 3 times already. Also the tax refund office was on 5th or 6th floor, I don't remember exactly, which was again difficult to get to as some elevators did not stop on that floor.
Overall, nice and relaxed atmosphere.