I recently moved from an e39 540i6 to this 550i sport automatic. This car is much more comfortable and "luxurious" while maintaining an even better balanced feel on the road (it is winter so i have not been able to push it real hard, yet). The iDrive requires some learning investment, but the payoff is real - you can set up a lot of the car features to your personal preferences. The back seat and trunk are larger. Only downside has been fuel mileage ~16.5 MPG in mixed driving compared with 22 MPG in the old car.
Comfort seats, iDrive, power, engine sound, heads-up display, bluetooth phone (once you get it configured properly).
Cup holders are still too small, storage bin well located but small compartments within compartments reduce available space.