I have the car for 2 weeks and I love it. The navigation system with bluetooth is a must it makes driving so much fun and I live in Los Angeles were I get the worst traffic. I got the 250 for gas mileage not power, but if you're not worried about saving in gas you should definitely go IS 350, it's worth all your dollars. The seats are very comfortable and my passengers are very happy. Some people suggested more rear seat room, but this is a sporty sedan and if you need tons of space in the back then get ES.
Navigation, ventilated seats, rear camera, GAS mileage!!! :), the interior and exterior design of the car.