I too am experiencing game immersion breaking graphical bugs in the game.
The original game worked perfectly fine on my AMD Radeon 7850 with a reduced framerate, no graphic screwups, at least none specific to my hardware. Any graphic problems that happened with the original game between May-August 2015 or so were game modeling/scripting/whatever bugs that mostly got fixed in later patches, like heads floating around bodies, people's bodies floating without movement, etc. But there were no texturing bugs or other things I'd consider game rendering or video driver graphics bugs.
When I installed Hearts of Stone a few months back under the GOG Agents program, I noticed the windmill's blades were graphically screwed up as if the models had incorrect vertices for some points, and the textures on them were all screwed up too. I might have spent up to an hour or two since then wandering around the game and noticed some parts of buildings and other objects in the game have fucked up vertices that cause horrid looking messed up graphics. The objects no longer look like what they are, but a convoluted 3D model that is all messed up. Sometimes it is just a portion of the exterior of a building or similar, and there are areas in the outdoors which show the ground or rocks or things jutting from the ground or landscape which are off kilter with misplaced vertices, or with missing textures causing it to just show up all black or shades of grey. Geralt can walk right into some of these things as if he is inside a rock with screwed up graphics or similar. It kind of reminds me of how screwd up Skyrim was in the mountainous areas where you could fall inside a mountain here and there or see behind the rock surface, see things floating above ground etc.
While it is true that technically my video card is below the minimum specifications which are for a Radeon 7870, the 7850 is technically identical for all intents and purposes and just a slightly slower card than the 7850, and it ran the game flawlessly since it came out so this is either a regression in the game itself with newer patches, or a regression in AMD's video drivers. I can not be certain of which is the case at the moment. Either way, it is a massive disappointment for this mind blowingly awesome game.
As it stands right now, the graphic screwups are so bad that while it does not prevent playing the game, it prevents me from wanting to play the game because they are terrible looking and immersion breaking. It is a great disservice to this amazing game to have such horrid graphical glitches show up this far into its lifespan. I updated to the current release when Blood and Wine came out and the problem did not resolve either. I have zero mods installed and did not have any installed in the game since it was originally installed, so this is not a problem caused by game mods.
When I'm able to do so, I'm going to start taking screenshots and/or screencasts of the broken graphics to post somewhere. Also I may try downgrading the video drivers back to last November or so to see if it is a driver induced problem.
Very very frustrating.
Peetz: It's easy to say that this is a bug. It cannot be, because I - among millions of others - are running the game without issue.
You need to check your computer hardware, installation or configuration. Something is not proper on your end. If it were a bug - then 100% of the people who bought the game would be affected.
That is simply not true. It is entirely possible for a game to experience bugs on one person's system and not another due to differences in hardware and the game taking different paths in rendering on the hardware. Additionally since there are a multitude of options available for the user to configure, a bug seen by someone may depend on the specfic range of options they have configured. It can also depend on what video driver options/overrides may be configured and many other variables.
People like to try to make out bugs as all or nothing, like they either happen for everyone out there or nobody at all - and someone claiming they're experiencing a bug while someone else doesn't experience it means they're lying or they created the problem or something. In reality, software and hardware is extremely more complex than that and it is commonplace that individual users or groups of users can experience bugs in games that multitudes of others do not experience, and it can in fact be a bug in the given game regardless. It could also potentially be a video driver bug, or a user caused issue of some sort, but to draw that conclusion ahead of time without any basis of reliable diagnostics proving it to be the case is simply blind sweeping a person's issue under the table with bias.
It's a game of hot-potato "blame the user" and not particularly helpful to anyone.