Not bothering to turn DOS games with no CDA-tracks to run without mounting any CD-images, especially when there wasn't even any need to use cracks to be able to run those games without the CD.

Not committing to keep whatever full installer versions around as unsupported extras whenever they turn out to be the last version to still work with this or that older OS that the later updates would no longer work with. Making games to run with modern systems is no excuse to start removing all options to continue to run them on older systems, especially any existing OS compatibility that the initial GOG release for each game was claimed to have.

My main issue with offline installers is that they rely on a temporary folder (which is on the system drive by default).
They need to extract straight to the destination, rather than waste space and SSD write cycles.

Otherwise I have no issue with localisations or Registry or anything like that. If anything I wish more applications stored their settings in the registry, as it makes it easy to backup multiple applications' settings in a single .reg file, rather than scouring for various config files all over the PC.

A large part of the reason for that is the Galaxification of offline installers, ie, for the newer installer format, the files are stored as Galaxy streams with obscure MD5 checksum style filenames, eg:-

tmp/53/4c/534c4f4b866e9544b57c638f388623f3
tmp/ab/d7/abd72c0dddc45f2ce6098ce3a286066a

etc. If you use InnoExtract to extract the (InnoSetup based) offline installer files using the switch --no-gog-galaxy, you can see the mess that the new archive format looks like on the inside. During decompression they have to be reconstructed (turning them back into proper files with correct filenames via an included 'manifest'). It's that extra stage that doubles the need for free space.

https://www.gog.com/forum/general/gog_standalone_installer_is_single_threaded_and_so_slow/page1
https://www.gog.com/forum/general/offline_game_installers_why_use_ctemp/post1
https://www.gog.com/forum/general/adamhms_linux_wine_wrappers_news_faq_discussion/post147

I've found many games newer installers slower than the older offline installer format equivalents (and the only thing changed was the packaging format not a game patch):-
https://www.gog.com/forum/general/dosbox_linux_support_dropped/post27

The problem is less that the localizations are there, but that you have to have them concurrent with your chosen language; it should be rather like a package manager: Pick the options you want, and throw anything you don't back into the sea. And I imagine that in voiced games, they easily add a good 1-30 GB per language, if not more.

The situation is so annoying that I prefer to use Inno Extract and https://github.com/Yepoleb/gogextract (for Linux), when possible, to "install" my games, indeed.
Just extract the files directly and create a directory to play it. I'd really vote for something like that.
Kingdoms of Amalur: Re-Reckoning, for example, has 42gb of game files, of which 20 gb (or more, can't remember exactly) are language specific audio files.

In this case, though, doesn't seem as GOG's fault, because you can't play the game if you remove those files from the installation folder. By that I mean the game crashes. Therefore this probably mean that the game .exe is hardcoded to check for these files, unfortunately.

Not sure what you mean. Not sure what you mean, did you need to fill out your list? Surely 640 should be enough for everyone.

I would certainly prefer if the installers extracted to simple file structure, basically being a compressed TAR file, or 7z file, with some simple xor encryption layered on it.

Kinda sad when you start preferring FitGirl repacks...

Er, that one should be obvious? And ties with other points too. Always installing the games instead of just unpacking in a folder and having everything there, settings, save folder, screenshots folder, whatever, so you can take it with you, or even use on multiple OSs on the same computer (in some cases the installation even makes it a problem to use, especially the same saves, on multiple users on the same OS), and when you're done with it you can just delete the folder and that's that, not hunting down traces possibly left by the uninstaller.

So, portability?

I didn't understand the permanence part.

Basically the part where the games will bury files deep in the system internals instead of being sandboxed.

That has a lot more to do with lazy game dev practices than GOG is doing on their own. Remember the time when all games wanted to install into the "Program Files" directory? Yeah, that kind of laziness.

A different kind of laziness; it was what allowed your programs to be Microsoft Certified or whatever. The fact of the matter is, you could box the resources in with a series of lazy symlinks.

Cymwhat? ;)

One thing I don't like that gog does is pander to the simp crowd. The softcore games (You know what I mean) don't really ever seem to bring in the best of crowds, and when they started selling them here, there was more of a drop off than there had been previously.

Pixels is pixels, man. The kids at work are telling me all the time how easy it is to hook up these days. Maybe people should try that instead of pixels...

Saying that, I was 13 playing LSL and having the time of my life back in the day, so maybe the problem isn't pixel junk, it's people in my generation not wanting the youngsters to have the tools we had to let steam off.

In which case this whole response is redundant and unnecessary. Sorry. <3

It's up to developers (both game & engine) to code for portability. Some games here are portable. Eg, Dark Engine (Thief 1-2, System Shock 2) games can run with .ini and game saves inside the game folder. DOS games are portable by default. ScummVM & AGS (Adventure Game Studios) can be setup to be portable by editing the relevant .ini's. For others though, they're at the mercy of the game engine. Eg, Unity Engine defaults to putting config settings into the registry under HKCR\Software\xxx then putting saves somewhere underneath %USERPROFILE%. The "Which 1 or 5 locations has it picked to save my game this time? Is it %USERPROFILE%\AppData\Local vs %USERPROFILE%\AppData\LocalLow vs %USERPROFILE%\AppData\Roaming vs %USERPROFILE%\Documents vs %USERPROFILE%\Saved Games" is annoyingly inconsistent, but stuff like that that's coded 'internally' to the game, it's up to the developers to change that (or let you change it) though rather than GOG. All the other stuff under HKLM\SOFTWARE\Wow6432Node\GOG.com isn't needed for / used by most games, it's just Galaxy meta-data.

Same with mods, some games like Banished & Stardew Valley save them inside the game folder, others like Torchlight put their mods in AppData\Roaming. Oblivion & Skyrim store their mods inside their game folder but look for their "Plugins.txt" Master list that tells them what mods to load under AppData\Local. You can use mklink to redirect some save folders to a USB stick (assuming the USB stick drive letter will be the same each time) using NTFS Junctions, but it's still not as "traceless" as a proper portable game as how self contained DOS games work (and would fail on FAT32 / EXFAT file systems). All those bad habits of spreading config / saves in half a dozen locations are the result of changes to Windows over time (single vs multi user, NT vs Win32-on-DOS (W95-ME) architectural changes, making \Program Files read-only unless elevated as Admin, etc), part inconsistent Microsoft documentation and part no standardisation between game engines. There's not much GOG can do when the config / save game code is internally hard-coded by the game.