Improved Direct3D 11 device interoperability via ID3DDeviceContextState, including the improved interop with Direct2D/DirectWrite
This alone for me has made this update worth it
EDIT: Just tested with SharpDX, theres some interesting debug messages now at least for D2D, if an object isnt disposed after the app closes (EVEN if it has been disposed with destructor) the process hangs and VS needs restarting, fortunately this worked out in my favour as I spotted a memory leak that must have been present for 6+ ish months, previous debug messages were not as good despite debuglevels being identical, visually it works flawlessly and faster now though.