Changes:
Good ones: Thinner, lighter, bigger screen, 2160/1440, i3/i5/i7 options, kickstand adjusts from 22 to 150 degrees and any angle in between. better scaling in photoshop. Dedicated new photoshop cc specifically for sp3. Better fan claimed.
"Bad" ones: Ntrig instead of wacom, stylus sold separately, requires battery, less levels of pressure sensitivity (256 IIRC), (may have addresed the edge accuracy issue, I don't know
But the presentation shows quite good feel and close to paper experience.)
Not changed: connectivity and ports, type cover still sold separately, still no slot for the pen,
Overall I think they have been listening to the customers and forum feeders regarding what's expected. Many issues have been addressed and a few have not.
I am curious why they have switched to n-trig though. May be lower cost and thinner layer of digitizer or something I have no idea about. But as long as it is accurate and feels like real handwriting it shouldn't be a problem except for those who require 1024 levels of pressure sensitivity as a primary thing.
Overall I think even without a next gen processor, the changes are enough to call it a next gen product.