Why is the Audi A2 considered a revolutionary car in its class?

I've heard a lot about the Audi A2 being ahead of its time, but what specific features set it apart from other cars in its class?

The Audi A2 was the first mass-produced, fully aluminum body car, making it significantly lighter and more fuel efficient than its competitors in the small luxury car market.

One of the major innovations of the Audi A2 was its clever aerodynamic design, achieved by reducing its drag coefficient to an impressive 0.25, which significantly improved overall efficiency and performance.