Bridgestone Blizzak tires turn the 135 into what is by far the most fun car I've ever driven in the snow. Turning off Stability Control leaves you with a fantastically playful and subtle Traction Control system which lets slides go just far enough to not get out of control. The seamless shifts of its Steptronic transmission permit opposite lock, up-shifts under power without upsetting the balance of the car or instant downshifts into corners to dial in the power for the exit.
The biggest difference between sliding the Bimmer and sliding my previous Mini and Saab in the snow is that rwd power takes the place of an e-brake. Instead of barreling into the corner as fast as you dared and pulling the e-brake to initiate a speed sapping slide, the 1 would prefer you get the nose to the apex of the turn and dial in power, and thus yaw angle, from there, accelerating the whole time. It's incredible.