I have driven the GS450h since 2007. It has wonderful, quiet, straight line acceleration. Passing and entering freeways is a breeze with the instant torque available from the electric motor. I drive a GS 350 when I have my cars serviced. I would not consider buying one after having driven the hybrid. The GS 350 lacks the quickness and quietness to which I have become accustomed.
One thing the GS 350 has that the GS 450h does not have is nice styling. For some reason the designers have scrapped the aggressive rear end of the GS/IS/ISF and made the 450h look like a TOYOTA AVALON. It may be part of the GS series but lacks the cool styling. The hybrid badges on the rear doors also look like an after thought and, as-near-as-I-can-tell, there is only one wood grain choice for the interior.
The wood trim choices also look like they came out of a BMW. That's not a compliment.