This video shows off the graphical changes in a nutshell. Lighting is totally gutted, geometry is simpler, spectral and bump mapping simplified or removed.
https://www.youtube.com/watch?v=ykbT03r_9Zo
They were showing off the better graphics as late as January this year on a PS3, and the downgrade in graphics is rather massive. This is certainly a much bigger issue than Watch Dogs, which seems to be making all the headlines. The neogaf thread is rather huge, if you're looking for all the details.
http://www.neogaf.com/forum/showthread.php?t=781625
Personally, even if the PC version has all the graphics in place, I'm apprehensive to buy it now. Dark Souls is one of the only games I really loved in
years, but I can't support this.