We have a service shop that specializes in BMW and MINI service, but also handles Mercedes and Smart. While we see far more BMWs for service, that is more of an indication of the market share that BMW/MINI has over Benz/Smart. Mercedes will also have a few bugs here and there and little quirks, and aren't bad cars at all, but will not have the handling and balance of the bimmer.
The more common problems for your car should be valve cover gasket eventually, water pump probably, and starter eventually. The water pump is usually a 1 time replacement, same with starter. Other than that, there could be miscellaneous coolant leaks, hoses, gaskets, etc, but again you will find that with any car.
Other than that, your engine is relatively bullet proof as long as you don't over heat the aluminum block. You know what they say, the grass is always greener until you get there.