Coming up on 13k on our R350. My wife and I love it, as do our two kids. We aspire to own only one car at a time, and this is the perfect choice -- great for hauling around the kids and their friends, but dignified enough for adult occasions. Plus it is remarkably fun to drive for such a massive vehicle. We've had it for more than a year now, and I still enjoy getting behind the wheel and going on long drives. Handling and acceleration are very good (considering the length and weight of the vehicle), brakes are excellent, and the ride is smooth. It's a mystery to me why MB hasn't made more of an effort to market this car. Yes, it's expensive, but for families like ours, it's perfect.
Parktronic is essential. Do not buy this car without it. Nav interface is something only a German engineer could love, but you get used to it. Info display in driver's console is useful. Power liftgate seems frivolous at first, but turns out to be quite handy. HK sound system is excellent.
The fact that memory seats are optional on a car this expensive is outrageous. MB might want to consider a bench option for the second row, to fit three across. Nav interface needs to be updated to touchscreen. Driver's seat is a touch on the stiff side. Needs more Bluetooth integration options.