I've owned my 2004 S4 for almost two years now (bought w/ 15k miles), sufficient time both to get over any new car puppy love and to notice any reliability issues. Well, I'm still in love and the only reliability issue was a balky sunroof switch that was replaced under warranty. At first glance, it appears to be a mild-mannered A4: solid German engineering in a conservatively styled sedan. But once you've settled into a front seat that holds you tight and heard the V8 grumble to life, you know this is no A4. A few corners at high speed and one highway on-ramp are all that's needed to confirm that you're driving an agile machine that carries speed deceptively well.
Handling. Power. Comfort. Understated styling
Larger back seat Better fuel economy (though this is a small price to pay for the exhilaration of 340 hp and pleasing growl of a V8)