After thoroughly enjoying my 3 series, I looked forward to the 530. What a disappointment, I have never had any car in for service so often, the high battery drain others have mentioned, iDrive replaced, tires have been replaced twice at no charge due to noise and excessive cupping, brake sensor malfunction resulted in having brakes replaced at 10K miles. While BMW has replaced all these items, having to take car in over 10 times in a year is just ridiculous. Not what you expect for this much money. Also just can't get this seat and steering wheel adjusted to point it's comfortable for more than a little while. All in all, a great looking car, and I enjoy it - when it runs correctly.
Styling, stereo system.
Tires, cup holders are useless in the front, more storage in center compartment and glove compartment, get rid of iDrive. Reliability, period.