I own an E90 and had a chance to sit in the F30 at the Philadelphia Auto show last week. The only noticeable difference was the ease of ingress/egress for rear passengers in the F30. It can be hard to get in the back seat of the E90, but much easier in the F30. That's the big area where the extra 2" legroom makes a difference.
Other than that, seat width, comfort, legroom etc were more or less the same. Definitely an evolutionary rather than a revolutionary car.
08 335xi Monaco Blue, '14 MCSc British Racing Green II
05 330Ci Convertible ZHP, Imola Red (sold)
00 540 sport, Orient Blue (gone, RIP)