From an engineering standpoint:
1. Has the suspension emphasized a greater degree of comfort than previous generations in their mission?
2. How do they feel about the current generation of fuel delivery on these vehicles? Do they feel it's been worked out?
3. What changes have been made to the braking system and what was their intent?
4. Did they learn anything from the e90 series, which introduced the first turbo engine since the 2002, that they couldn't take advantage of in that chassis/design but now can? I.e. better placement of cooling ducts/air intake/oil coolers? Looking for improvements from the e90 that specifically relate to engine life, performance, reliability/longevity, etc.
5. Any fancy new stuff done with the valvetrain itself? I.e. I think the e90 introduced hollow magnesium cams (I could be wrong) with their new engine. What's different with the new 335 from a powertrain perspective from the last e90 335i?
Just thinking off the top of my head. I don't really read the new 3-series as having changed alot from an engineering standpoint - it's more "I'm bigger, weigh less, look better, and have better interior design" and less "I have a revolutionary suspension"
F80 m3 - 20k miles as of April 2015....08 535xit - 120k miles