This is a wonderful car. I have the 2.7 twin turbo motor with 6 speed manual, it is a joy to drive. You can drive it as smoothly as any Rolls Royce around town, but punch it and let the turbos spool up (pretty instantaneous spool up) and it takes off like a rocket. It cruises at 100mph with total ease in 6th gear, and passing is no problem. The mileage is also very reasonable, at 21.4mpg average (and I drive fast and in town a lot).
The interior and stereo are great. The black leather seats are comfortable and roomy and there is lots of storage space. Both driver and passenger seats have memory as well, which is nice. The standard CD player and tape player are clear and offer plenty of adjustability (treble, bass, mid etc). The back seat is also very roomy and 5 adults can comfortably ride in the car.
The Xenon headlights and Quattro AWD make me feel really safe driving in even the wettest conditions. The A6 is very confidence inspiring. The ABS is also very good.
I only have 2 gripes with Audi in the design area. First of all, the shifter has sort of a long throw, not terrible, but shorter would be really nice. The other thing is that the car is a bit understated for how fast it is. They remedied this for 2002-2004 models with nice exposed tip dual exhausts (the 00-01 have dual exhaust, but the tips are hidden) and a nice facelift. I think with a light body kit, deck lip spoiler and some more thrust the car would look a lot musclier.
Overall a great car I recommend wholeheartedly, it's fast, fun and very luxurious all while being a very good deal used (mine cost just over 20k).