Dazelya: Same here. No guys, u don't need to download the game :) Just copy discs on your computer after that just rename them like;
SETUP_TH.BIN to SETUP_TH-1.BIN
SETUP_T2.BIN to SETUP_TH-2.BIN
use same way all discs (TH-3, TH-4, TH-5 etc.) gl guys and sorry for my English :)
I did try to copy the content on the disk over to my HDD, however i did not rename the files on the disks.
Got a response from GOG support they started to nag about a faulty nvidia drivers and so on. So i did a driver clean with DDU (Display driver Unstaller) in safe boot before installing the official witcher 3 drivers from nvidia. Thought it cold not hurt.
They also wanted me to do a system restore In Windows 8 I did not see the point since my computer dont have any problems installing any games or software from disc.
CharlesGrey: I know things take time (installed GTAIV from DVD disks some weeks ago) but when the installer dont do anything and does not even create a Witcher 3 install folder you know something is really wrong.
But all is good now I have downloaded the game and it is running smooth 60fps on ultra at 2560x1600.