Drove an '03 E39 540i-Mtech for 5 years. Great car with serious grunt. Wanted an M5, but didn't want to deal with manual transmission during business calls from the car. Sold it about 6 years ago. Might be the best daily I ever had and I still miss it, but my 2015 Cayenne diesel is closing the gap. Especially after averaging 74 mph and getting 31 mpg on a recent trip.
The E39 still looks great to my eye, especially with the m-parallel wheels. The lack of bluetooth and dead pixels in the message displays get annoying, but there was a lot of forum support for the cars to help work around these issues. Probably even more now. Beware of VANOS issues and plastic bits wearing out in the engine bay.