^ this:)

Alright, that's a problem. It comes from the fact that ScummVM simply uses the original datafiles and doesn't do any checks for CDs, meaning those files are merely what was originally on the disc.

As far as I know, no. For some games, you can configure ScummVM to use their original save menus, but the save system will still be that of ScummVM itself.
It doesn't copy them. It just reads them directly from the directory you specified.
That's true, but it's as close as one can get to running these games in their original, unaltered states on modern systems.

That's weird. The 7th Guest works fine on mine without anything mounted.

ScummVM doesn't "change the executable" in any sense of changing the core game. In fact, it ignores the original .exe file and just loads the data files. Eg, in Sam & Max Hit The Road, you can delete / move all the .exe's out of the dir and the game runs just fine. All ScummVM does is load the data files directly from wherever you installed the game without touching the original .exe. Any save games it creates are just for ScummVM, but you can continue to play the "vanilla" game in DOSBox without using ScummVM and it'll use whatever original save system was there.

For me, it's better in many games. Eg, graphics and subtitles look less blocky with HQ3X AA setting vs DOSBox, aspect ratio correction, ability to vary the subtitle speed, better save/load dialogue boxes, faster quick save/load (ALT/CTRL 0-9 keys) even in games which never originally had that, better MIDI support, better video / cutscene scaling, easy ability to take screenshot's, Global Main Menu, etc.

There's no real one big thing but rather lots of little things combined, and even then many are optional. Eg, in The Neverhood there's an option to skip the 40-screen Hall of Records storyboard screens. If you don't want that, leave it unticked and it'll play like the original. If you want the "pure" version, play in DOSBox. I haven't noticed any difference at all in any game that made anything worse or less reliable.

So if I use the game's save menu, it's still ScummVM files that are being saved/loaded?

I don't really care about whether the save games are in the original format, or ScummVM's format. My only concern is that I don't want the games to become too easy but adding a save-anytime feature. If a game didn't allow saves, or only allowed saves in certain places, I want to play that way too.

So basically, if I use the game's menu to save, and the game does allow me to save, then I can assume that the original would have allowed me to save in this particular place too (even if it's actually ScummVM doing the saving now)?
EDIT: when I launch in DOBox, and after getting the sounds to work, I get this "Please insert Disc 1" as soon as I load the game.
Is the disc images somewhere in the GOG files? I couldn't find it if so.

In my experience, yes. I've never noticed much of a change in that regard for the games I've played in it.
Changes/additions like that really depend on the game in question.

No, not at all. ScummVM just uses the game's asset files and ignores the game's own executable completely. It makes no changes to any of the game's files whatsoever. You can run the same game through both DOSBox and ScummVM from the same folder.

Hmm, maybe my memory is failing me or then it's just that its been some ten years and a lot of games have been added since, but I thought that at a time there was just one game that didn't have copy protection disabled and then they found an official version of that without copy protection too. So, it wasn't exactly uncommon and I don't think my scummvm library has a single game that still has it on by default. You can turn it back on, though, if you like.

I still have all my old PCs from the 90s :). I connect them and use them occasionally to play the old games that I own. Sadly, GOG doesn't offer original installation media, and spending a (relative; compared to GOG prices) fortune on the original CDs just to play that one game on it, is not worth it. And trying to transfer the GOG version to them is not always worth the hassle. Like InfraSuperman, DOSBox is good enough for me.

Btw, is there a Gogmix that lists games using ScummVM?

Thanks for the DOSBox fix! Do you notice any differences running 7th Guest in DOSBox vs. ScummVM?

From what I noticed (and I didn't play very far using DOSBox), the music during credits during the intro is missing. For the rest of the intro and during the game itself, the music plays normally in DOSBox, and no other differences were present as far as I could see. I decided to go with ScummVM after all.

I imagine that's just the Gog's version problem, however.

I was thinking of creating one, but I don't feel like it since GOG does mention which games use ScummVM, unlike DOSBox. It's just not possible to filter by it.

Ah, too bad, but thanks anyway.