My wife was given this as a loaner for her E350 while hers was serviced. I fell in loved with the E550 its a BEAST. You get luxury on top of a Sports Car.
I own an e550 coupe. I love the car, it's fantastic. But two caveats: the c pillar makes a HUGE blind spot. dangerous, in some situations. And the seats are not very comfortable for a high end car. My partner has back problems, the seat is not good for her on road trips. Reliability over 5 years/70K miles has been very impressive.