2022 Update to you

My 2 cents; a lot of GoG games that SHOULD work in XP do not.

Originally XP compatible games GoG version Don't Work in XP:

Dishonored
Tomb Raider 2013
Deus Ex Human Revolution
Crysis ---------------------------->Original GFWL Retail Disk Version DOES Work
Star Trek Bridge Commander---------------------------->Original Retail Disk Version DOES Work
Star Wars Battlefront ---------------------------->Original Retail Disk Version DOES Work
Star Wars Battlefront II---------------------------->Original Retail Disk Version DOES Work

XP era games of which GoG versions DO work in Windows XP:

ArmA Cold War Assault
Dragon Age Origins
Fallout 3
Gothic III
Hitman Blood Money
Mount and Blade: Warband
Neverwinter Nights
Neverwinter Nights 2
Serious Sam 2
Star Wars Jedi Knight II: Jedi Outcast
Star Wars Republic Commando
STALKER: Shadow of Chernobyl
TES III: Morrowind
TES IV: Oblivion
The Witcher 2
Tom Clancy's Ghost Recon
Unreal II The Awakening

other Non-GoG games that still worked via disk version

Civilizations: Rise and Fall CD
Doom 3 CD
Enemy Territory Quake Wars CD
Far Cry CD
Far Cry 2 (Direct2Drive digital downloaded version still works)
Gears of War GFWL Disk Version (must do date change fix to system DTG for game to launch)
Microsoft Flights Simulator 2004 CD

Overall I am not happy with the level of meddling by GoG with games that previously worked fine in Windows XP.

It does suck a bit when a GOG game that should work on Win XP does not, but it's a price to pay for them working on the current systems.

The main problem is that you won't know for sure until you try, as this detail is not listed anywhere. Another game I encountered like this was The Suffering. Disc version works flawlessly on XP, but the GOG version does not launch.

That's not what GOG does though, you want the original versions then get them off ebay and patch them.

A few games require game files to be modified to call more modern things, codecs for example, older games might call them and 10/11 doesn't work with them so they have to change it to get it working under 10/11 but than XP then can't run it as its doesn't recognise the newer codec so its it be expected.

Edit: Also Serious Sam 2 is not on GOG yet. Its Second Encounter you might of meant a different game.

Whilst you're correct that some things have needed updating for codecs, etc, 99% of retaining GOG version compatibility of old games on older computers they were designed for lies simply in not deliberately breaking compatibility on purpose in the first place, eg, by recompiling older games with retroactively added Galaxy achievements (that originals never had) for offline installers (that people use precisely because they don't want achievements...) that require bundled Galaxy dll's that in turn require W7 (eg, Fallout New Vegas) has to be the dumbest way of "enhancing" old games imaginable vs having Galaxy just download 1-2 extra Galaxy exclusive files that adds achievements only for Galaxy users that want / can actually use them.

Likewise, GOG spent a lot of time removing .exe's from DOS games that were packaged with ScummVM then retested only to have to go back and waste even more time adding them back in again and retested again to avoid a "Pirates 1, Paying Customers 0" situation by driving paying customers to "Abandonware" sites anyway just to get the missing game's .exe's if they wanted the option of using DOSBox. For many such examples, there's actually far more effort involved in breaking compatibility for stupid artificial reasons than simply leaving them working by doing nothing, and a lot of us can clearly see the difference between an old game that stops working for unavoidable genuine compatibility reasons of an ageing OS vs entirely manufactured 'unwanted 3rd party online branding in offline installers' avoidable ones. (Something that also affects new games on new OS's...)

It wouldn't be as much of an issue if GoG support was as responsive/dependable as Steam is; but for me if the GoG version is broken (across any operating system or specific to XP) then I might as well just buy it on Steam where I'm guaranteed a rapid refund if the game doesn't work if I'm not going to use XP.

Useful info to me and something I'd expect from professional stores...
Anyway, Who else than hobbysts are going to save the day when needed?
Thanks for sharing charlemagne1980! and keep those XP machines being productive :)

Actually, Descent is a WIndows 95 game and a Mac OS 7.X game. Descent II came bundled with the PowerMac 6500/300 I got in 1997, well technically my mom bought it through the school she worked for since both our respective schools used Macs.
It just happens to be one that worked with Windows XP, although there were quite a few games that did not because of the NT architecture instead of the 9X one.

That said, I was able to install the following on my 22 year old XP computer:
Avernum series, Beneath a Steel Sky, Eschalon book 1, Fallout Fantasy General, Flight of the Amazon Queen, Heroes of might and magic II, Konung, Lure of the Temptress, Might and Magic I-VI, Silent Service I and II (not III, but the machine is too old to meet the requirements), Ultima I-VII, Wizards and Warriors, Sid Mier's Colonization, Divine Divinity, Silent Hunter II, Teenagent,
Unfortunately, none were installed after 6/6/2020, so if something has changed I can't help you.

That is not,,,and never has been the case. GOG tweaks the games to run on a modern computer..if fact, that is the foundation of their business. Alhtough they play the same as the original "under the hood" they are different.
Sometimes in tweaking the game to run on a modern system, they have to make changes that might make it difficult to run on an older system.

Descent was a DOS game . After W95 came out, the compnay did put out a "Windows" verson that was just the DOS game in a Wndows 95 wrapper. This happened to quite a few dos games.

Thanks for this, this behaviour flies in the face of what GOG set out to do in the first place. If they had working XP installers, why mess with them? Why not just have separate installers for different OS? Why break support that they had working originally. This has driven me to archive.org and abandonware sites to source the original discs and deal with cracks for pervasive DRM, something GOG set out to "fix" years ago. The XP era specifically is the worst for malicious DRM, and it seems GOG can no longer help with getting these kinds of games working.