We currently have a 2009 Mercedes Wagon with 15k miles on it. Also for context we have a Toyota mini-van and a Prius.
This current wagon only seems special when you are on the highway. There it is in it's element. Extremely smooth, quiet yet with the classic German feel. Other than price it isn't much different from the Toyotas.
Overall build quality actually seems to be less than the Toyotas I am sad to say. We have had a number of minor problems with the electrical and mechanical systems. The CD player still doesn't work. The right windshield wiper stopped working etc.
In general it seems as the though the car is several years behind the competitors in features.
I have always wanted a MB wagon. I have not been disappointed. Solid and reliable, quality constructed both inside and out. Great handling for a wagon. Only service has been 1 year standard service. The nav system could be easier to use, but ut us on the mark.