I have had my M3 for almost 2 years now and absolutely love it. It is powerful, agile, looks great, and still feels solid even with 113,000 miles on the tach. Only a few problems; ac is very weak and some of the LEDs on the dash are going out, but hey, the car is almost 10 years old. I love how my M3 communicates with the road; the newer BMWs aren't as in tune with the driver. It definitely inspires confidence on the track, although winter driving is very scary. If you can afford to, have a different car for the winter (if you live in a state like Colorado). I plan on driving this car until the wheels fall off. By the way things are looking, that will be a very long time from now.
Power, handling (like it's on rails), build quality, looks.