The QC Ultra Gen 2 makes adjustments to the fit, battery, and design of the headphones, and adds a lot more in terms of audio modes and customization. While that sounds overwhelming, the majority of these changes are minor, meant to be imperceptible to general audiences. Bose really took an "if it ain't broke" mentality and it has mostly paid off.
The QC Ultra 2's defining theme is that it doesn't attempt to rewrite Bose's legacy but rather tidies it up. They look identical to the first generation, except for the yokes, which swap a matte aluminum finish for shiny polished metal. The QC Ultra 2's earcups are slightly shallower than those of their predecessor, which can cause fit issues for people with larger heads and ears.