From an engineering standpoint, it was basically a race car for the street. The aluminum body was mounted over a tubular frame, not unlike what you'll find on most purpose-built race cars, even today.
Countach became the first production car with vertically-opening scissor doors. Gandini had earlier used them on the also-iconic Alfa Romeo Carabo concept a few years earlier, but no car entered production with them until the Countach. Hence the term "Lambo doors."
The very last Countach was produced on the 4th of July. The last Countach was born right as the first Diablo was being built. It never made it to America, though, going instead to Lamborghini's corporate museum.