There were a number of software and electronic problems that plagued early versions of the 04 model. In addition, some people complained about stability in cross winds and problems with run-flat tires. BMW has been resolving these problems quickly, but alas, not always to the satisfaction of early owners. My E60 was planned for December 2003 build, but the dealer convinced me to wait for the updated March 2004 production and I'm glad he did. The only problems I have are software related, namely lack of MP3 playback, removal of RDS, and removal of FM Autostore. BMW has deleted 2 features that I used routinely. This is NOT good business practice so I have sent a written complaint (along with praise for everything they did right).
I have driven a number of cars including 2 Honda Accords previously owned by my sisters, 4 Lexus models currently owned by the women in the family, 2 Nissan Maximas I owned after college, and a variety of rental cars. My opinions:
1. Nissan Maximas are drivers' cars in the same tradition as BMWs. Well put together, exciting to drive, wonderful steering feel.
2. Lexus and Toyota are made in the tradition of Mercedes: Soft supple ride, minimum driving excitement, compromised handling, very conservative interior. I rented a 2004 Toyota Camary recently, which proved to be very disappointing in brake feel, steering stability, instrument cluster, and cornering.
3. Honda and Acura are also more in the BMW tradition. Very minimalist designs, but fun to drive with good steering and suspension feel.
For me, without question the most enjoyable and satisfying driving experience has been with the three 5 series I have owned: 97 528i, 01 530i, and 04 545i. The 01 through 03 E39 is a FANTASTIC machine, but the 04 545i is easily the BEST car I have ever driven. Spend a month behind the wheel of a 545i and you'll know what I know!