I've had my IS350 for over three years. It's one of the best cars I've ever owned. I love the refinement, performance and build quality, although I have had repeated issues with the sunroof not closing and rattling when open. The middle speakers on the front doors leak air, specially if the sunroof is cracked open. Cold air can be felt blowing on my knee in winter. I was told they all did that!
Performance, exterior design and quality.
I would suggest the trunk lid and doors be aluminum skinned (the hood already is) for lower weight. Also, if the Traction control is to be allowed to be turned off, then a limited slip differential is a must! In manual mode the transmission should upshift when commanded, with no delay!