I had this car for a 7months. This car has the best utilization for a super car. I considered Porsche 911 turbo, Audi R8, and Ferrari F430, but with a family, those cars are unacceptable. Considered Alpina B7 but, shaky reliability and it being non-factory car, I disqualified it from my list. I opted for S65 AMG for performance and 4 door convenience. I have not regretted choosing this over Porsches or Ferraris. Until Porsche Panamera or Ferrari comes with a four door sedan, this car has no competition. Plus reliability wise, MB is a far better choice. For now, this is the only choice for supersedan.
Great performance for its size. There are no compromise and this is by far the heaviest accelerating machine I have seen. Unless Ferrari can build a sedan that outperform F430, this is the best performance sedan. I had E55 AMG and older M5. They were good but, lacked comfort.
Gas mileage is a disfunction which is not neccessarily considered for this price range and category but, it is dreadful. Noise level is quite high for ultra luxury sedans. Muffler jidders and rattles a bit too much in acceleration.