I'm not sure where you have heard bad reviews on the RX400h. Consumer reports rates it as one of their top SUV's (hybrid or not). I have both an RX400h and an '06 GX470. I love both cars. My RX400h has 8500 trouble free miles on it. Smooth as silk, quiet, great acceleration, super transmission (CVT) and superior gas mileage for a powerful luxury SUV.
My wife however is a BMW lover. We traded in her '04 BMW X5 for the GX470 (the RX400h was my everyday car). Well guess what? I now drive the GX470 and she is driving my RX400h. She has already informed me that we are buying a new X5 next week. (For the record, her old X5 had 22,000 miles on it and had only seen the dealer once at about 13,000 miles for regular service (paid for by BMW). Given the choice between the RX400h and the GX, I have decided to keep the GX, but only because I need the additional seating (I coach youth sports, basketball and baseball, need I say more). So it looks like I will be trading the RX in, but through no fault of the car.