I had a VW 1600 engine that needed to be torn down. And I had a camera. Now, you have a photo gallery of the innards of that engine, which makes for an easy walk-through of the parts make your car go.
VW engines are crazy efficient, they almost never need any service. I have seen one driven over 30,000 miles on a busted crankshaft. Try doing that with a Ford.
The air cooled VW engines were designed to be very light weight and simple enough to be completely re-build-able by the owner with a minimum number of tools. They were also easier to manufacture because they didn't require large castings and had fewer parts. The big mistake was to put the little 1600cc engine in a VW Transporter Camper with a pop up top. (I know. I bought one. It struggled up moderate slopes or when driving into the wind.)
The flat, air cooled engine was used in different cars, trucks, Things, and tractors. (If you don't know what a VW Thing is, ask your parents.) It was also used in Porsche cars for a long time.
They're not all that fuel efficient or powerful, they're just light weight. A water cooled engine of equivalent output would be smaller and might be used in a better quality lawn tractor.