Just anecdotal and not related to BMW but the worst vehicle I ever owned was a 1998 Mercedes ML320. IMO it was because this was Mercedes first foray into US-based mfg and a first year product - so it became the perfect storm! So just because we are talking German know how does not mean there might not be a misstep. I know this was Mercedes :-)
Have not owned one since and never will...
Current Ride - 2011 328i Convertible - AT, Nav w/Sirius, JB/Cream Beige
Past - 2008 BMW 335xi Coupe (ED), 2003 BMW 530i, 1999 BMW 528i