This car is just a redesign away from coming back into people's minds (think IS-redesign; now with split-fold rear seats); however, differentiating it from the ES will be the major issue. It's a BIG car, and the limitations (including no folding rear seats!) don't help. I think it'd be better if they made it the same size as the ES, but more sporting compared to the ES's comfort-first nature.
The IS sells well as a luxurious, but entry-level (and priced!) Lexus. The ES sells well as a comfortable, luxurious boat of a car. The GS is just getting expensive (a relative bargain is still a lot of money) and does nothing better than its competition for many reasons.
...one of the biggest issues is that nobody can ever tell it apart from an ES! They look so bloody similar...