Ride is compliant on the 528 and 535. it is much, much better than the 3 series. it's softer than the E60, but IMO from my 2011 F10 535xi there was not that big of a differece. the car was comfortable. i traded and went wit the 550xi with sport (not an M-sport) with it's adjustable suspension settings and the car is extremely comfortable.
from a person with a bad back, and a bunch of joint problems, the F10 is comfortable. I wouldn't get it though without comfort seats.
Auf Wiedersehen 12 550xi