Superb V8 that revs like the dickens all the way to 8k rpm. Stock tuning is a bit weird when not in Sport mode, as you can really feel the power being limited down low. The throttle is extremely responsive in Sport mode, and really adds a sense of urgency when driving. I only test drove the M3, but the two engines seem to be pretty similar. I'd give the nod to the Audi V8 for a bit more torque and rev-happiness. The Audi V8 also has a much throatier, deeper sound. The M3 sounds almost artificial in comparison. Shifter felt a bit long and sloppy at first, but I was coming from a Miata with a short throw kit, so that was to be expected. As I've gotten used to the car, I've found the throws to be perfectly acceptable, and while the shifter may not engage as positively as I'd like, there is still enough feel and positive engagement for those looking for it. The shifter in the M3 is absolutely shameful. It seems BMW has focused all their efforts on the DCT transmission, as the shifter in the BMW wouldn't have been out of place in my dad's Dodge Ram.
Handling is superb, as one can expect from quattro Gmbh. Planted and secure are the first two words that come to mind. Very responsive direct steering feel. Very firm ride that isn't helped by the 19" wheels. I feel like 18s would have been a better compromise between ride quality and handling. That said, it's certainly more than acceptable considering what the car is designed to do and how capable it is.
Seats are equally superb, if a bit cramped in the back. Much nicer than the M3 seats, with better bolstering, and higher quality leather compared to BMWs "leather" interiors. While not necessarily the vaunted "cockpit" interior that is supposedly the gold standard for sports cars, the interior is a notch or two better than the M3s and doesn't seem to slope away from the driver. Quality of materials, as well as overall layout seem to be just a touch better than the M3s implimentation. Whereas the M3 interior might be described as modern and minimalist, the Audi interior feels more tech-y.
EPA ratings are accurate. I've seen as low as 12 mpg in the city, and up to 22 mpg on highway journies. I average 15 mpg in mostly-city driving.
Subtle exterior styling. Flared wheel arches and side skirts let you know that it's not your everyday A4. A pair of 'RS4' and 'V8' badges and oval tailpipes are the only other clues to let you know that it's a 420 hp animal. Compared to the M3, it's restrained. No hood bulges, side vents, or carbon fiber roof.