The GS certainly is a fabulous car, especially the 450h. It was on my list but overall the NX did it for me.
Most of the reviews for the NX were average at best but you have to experience it for yourself. For me the NX fulfills my criteria.
The only impartial detailed reviews I read were in CAR magazine and Parkers. The other magazines are German owned and more or less slated the NX.