Overall
I live in MA so AWD is great to have, if not, a necessity. I looked at the BMW M3 at the same time as well but it failed in the winter comparison (it would be garaged all winter). So, I bought this new and have been delighted with its performance and amenities (eg self-dimming mirrors!). It has been very reliable. I've put over 50k miles on it so it's been and gone through warranty. I got the free servicing so I have no idea about service costs but beware it takes a lot of synthetic oil every time. I've taken it to all of the major race tracks in the NE and had a blast charging round (Audi Club). You won't beat an M3 off the line but on a winding track you'll beat it in overall time. Fit and finish in the cabin is the best in industry.

Concerns/criticisms - if you want a flashy 'look at me' car then this is not it. If you have to carry adults in the back seat all the time then again this is not the car. If you have to cover long miles cross country on the highway then again this is not for you. The sports suspension is just too harsh for long hours in the saddle.

Updside - great fun to drive. High quality fabrication and finish make it a joy to own. The stealth side of its performance is an advantage. If you're going for one then don't buy the tiptronic unless you are a stop start driver in the town all of the time - it saps so much of the power and fun

This is honestly the best car I've ever owned and I've had civics, 2 3-series, a 5-series, an older A4 2.8L, and a Volvo 240. The 2000 S4 6spd is an unbeatable car. It has all wheel drive (which is an amazingly grippy feeling whether you drive on dry, rainy, or snowy pavement), incredible acceleration, and looks to kill. The shifter is smooth, the seats keep you in them, an the stock sound system is wonderfully clear, having a far more full range than I'm used to hearing in unmodified sound systems. The suspension provides a smooth ride, yet leans very little in corners. This car is SOLID, and if you don't hammer on it too much (which is nearly impossible) you can get around 28 highway miles per gallon consistently. City is a little worse, as is to be expected. With 260 ft/lbs of tourqe at a mere 1850 rpms, this twin-turboed 2.7L V6 pulls no matter which gear you're in. Pass someone beginning at 50 miles/hour in 6th? No problem for this car. Although it's power really starts up around 3000 rpms, it has no trouble getting up to three, with VERY little turbo lag. The best part of this engine, I would say, is that you don't have to rev it all the way up to get power out of it. Shifting after 5500 rpms is almost couterproductive. I always say that's a good thing, because the fewer the revs, ceteris parabis, the less engine wear.
Buy this car.