I would question the notion of finishing a game in one sitting. Most games weren't designed to be played that way, there's a save function for a reason. You maybe play one evening, and maybe pick it up again a couple days later. If you think you're gonna forget stuff, write notes.
I'm not talking about deliberately hurrying through a game here, but rather games which are designed to be an experience which can be completed in one sitting. Same principle as a movie. Of course you can stop a movie at any point and resume it later, same as any game, but some games lend themselves to being played all in one go. That is what this list is intended to uncover.
I'm fine with suggestions where the main quest can be completed in one sitting, but where there is more content that can lead to further playing down the line. Or games where the replayability is high, so that another playthrough uncovers different things. Again, this list isn't meant to collate games where you can suck the joy out of them by rushing through them. It is for games which are a worthy way to spend what little gaming time one might have in their otherwise busy days.
Thanks for all the additional suggestions folks, I'll update the master list as well as the GOGmix.
Thanks, Zombies. is a great suggestion, that was a one-day game for me as well. I can't in good conscience list Rogue Legacy however, since personally I've been picking it up for stray hours over several evenings and still not defeated the first boss. Perhaps my skills just aren't up to it, but if you beat this in one sitting, you should think about gaming professionally. ;)
Fahrenheit can easyly be finished in six hours for a newcommer.
It´s a very intense, but very short experience!
I still haven't beaten this one, keep losing based on stress level. I expect it could be completed in one go once one got good at it though. I'll put it on the list.