I have had my 2003 Mercedes-Benz C32 AMG for a little over six months. I love the engine, it seems to be put together rather well (I haven't had any problems in 4,000 miles), but the interior is awful. The ac/heater/wiper/c.control/pwr seat controls are worse than in the 1990 Nissan that I had. The cup holder is only symbolic, the lack of navigation and an in dash multi disk CD player is absurd at these price levels. If I could have taken my 2001 Saab's interior and put it into this car it would be perfect. Fortunately as soon as you put your foot down the thing takes off!
The engine, taut steering, build quality (so far), very good transmission, and engine sound.
Completely redesign the interior (copy Audi or Saab if needed) and make the rear seats a bit bigger. Get the seat controls off the door, make navigation and variable speed wipers standard. The seats need lumbar support! Again my 1990 Nissan Pathfinder had a better / more useful interior.