Quality is a keyword for BMW and always has been, but its interior feel can be a bit dark and cramped; all of these elements are present in the cabin of the 2011 M3.
The front sport bucket seats offer plenty of room, but thigh support is lacking, and there's not much room in the footwells on either side. The rear seat is best reserved for occasional use by adults, though some (likely smaller) passengers may find it just fine.
Beyond the top-notch build quality and materials, there can be a bit of noise in the cabin--the wail of the V-8 raises in both pitch and volume as you step on the gas, though in a sports car, it's hard to call that a fault. The wide, grippy tires can drone on some surfaces, though for the most part it's nothing to complain about.
Optional trim upgrades of carbon fiber, wood, or aluminum allow customization but don't much brighten the somber experience.