Hate the digital gauges - mostly the temp and gas. Notice how the needle on those is like 1/2 length? Drives me crazy. No reason they couldn't make this right. Either way, much preferred the old one. Note, it does not save weight from what I'm told - it allows BMW to use the same cluster in all cars.
B&O sounds better than any stock stereo I've ever heard. Changing out a stereo in a BMW is an expensive effort coupled with a voided warranty. The $3,700 is low cost compared to that and much lower than the Audi B&O at $5,900 that sounds terrible. I'm really glad my car came with it as I too was going to skip this option and hope the 2015 with HK sounded better than stock. So to me, very much worth the extra money (once again, not saying it is perfect or near perfect sounding - just the best stock stereo I've ever heard).
Ride comfort - I have not noticed a jerky shift at all in sport mode (have not done sport +). I will say that in comfort mode, I've got severe lag that just does not exist in sport mode.
Steering feel - can't compare as mine is hydraulic - however I find mine to be perfect as well.
Adaptive Full LED - incredible. Worth every penny. Even more so for how they look on the car. Totally recommended.
Fineline Oak wood trim - the 2nd best thing next to piano black. Not sure where/who thinks it makes it look like a Chris Bangle car - but it is a nice compliment to a very nice interior. The other choice looks much worse and I agree Aluminum is out of place in this car.
Navigation - so fast compared to other cars. Agreed - perfect - except for zooming in/out as that is STILL reversed
PS - I think you meant to say the 650i has fatter tires. But the ultimate reason the 650i does not ride as nice or take potholes as good is that it has low profile 20" vs the 18/19 on the 335i. So much less sidewall to absorb those potholes. Rumor has it a switch to a Non RFT does wonders.
edit - the 650i has wider tires and a shorter sidewall. You probably meant fat=tall sidewall. But I don't think tall people like to be called fat