Bought used at 40,000 miles now has 112,000 miles. Fun to drive. Solid, no squeaks or rattles. Replaced 3 sensors, one of them twice; always $500 a pop. Replaced gasket to stop oil leak and burnt oil smell but hasn't worked. Some front end alignment issues also. No AM radio reception. First foreign car I've owned, not sure if I'll stay with Audi; more expensive maintenance than my previously owned Ford products.
Quattro drive system and overall handling.
Obviously Audi has some quality control issues to address particularly with electrical devices, gaskets, etc.