Fast - Do not forget that this started life as a racer. When it premiered, it was the fastest VW powered airplane ever seen, 30 mph faster than the previous (retractable gear) contender. KR's appear to be faster for the same displacement, but it's still pretty speedy for the horsepower.
Adaptable - One place or two. Stretch or standard. Original low wing, or roomier, more stable low wing. You choose.
Versatile - You can stunt it. You can land it on grass (taildraggers only). You can get in and out of 1500 feet without scaring yourself to death. With ear plugs and an auxiliary tank, you can fly it for as long as you butt will hold out.
Cheap - Under $10K for materials, including engine, is possible for a careful scrounger, and $20K is easily achievable. Complete, flyable airplanes can be less than that.
Standard Aircraft Materials - There is nothing in this airplane foreign to your average A&P. This means you don't have to do your own repairs if you don't want to. Everything is inspectable, and repairable using easily obtainable materials and skills.
Common Enough - Enough were built and flown to work the bugs out, create a used market, develop insurance experience, and cultivate builder and vendor support that continues strong to this day.