Just bought the E550 4matic a week ago. Love the car. It came down to the audi A6 or 5 -series. This car is much better in both build and drive. The V8 is very fast and smooth. The HK sound is awesome. The Xenon lights are great! Once you use them, you won't like regular lights again. The only things I haven't liked is the COMMAND function. It's ok to use. More complicated than it needs to be. The IPOD interface could be better. I got the sport edition. Not much difference in ride quality between sport and comfort modes. The car height feature is pretty cool when parking near a curb. It raises the car about an inch so you don't hit some concrete curb when you park.
Sound system is a 10! V8 engine. Interior and ext are excellent. Chestnut brown leather is much better than standard color leather. Lights. Keyless entry is cool.
The seats are not as comfy as the 5- series. More firm and ergonomic. Don't know if this is in sport model, even with drv contour seats. Seats little better after 1000 miles. Folding side mirrors. Better ipod function. ie play radio through iphone, improved track selection and not through glove box