The cities offer convenient public transport (underground trains which arrive every few minutes). In rural areas you are lucky if you can catch a bus once a day ;) You are pretty much dependent on your car.
Cities offer a variety of stores, while in the countryside you just have a few. I suppose the difference between rural areas and cities in Germany is not much different compared to other countries.
Things that might be different to other countries:
Rural areas are often not too far away from cities. Let's say, even if you are in a rural area you usually need just an hour by car to get to the next city (approximately, I just want to say that the distances are not that huge).
You usually have internet connection in rural areas as well, this might be different in other countries.