I.e., games that hooked you in and you couldn’t stop playing until it was finished. Not games that just happened to be unexpectedly short. And by “completed” I guess I mean the main story etc, not 100%ing the game :).
For me, it would be Catherine, Bioshock Infinite and Black Mesa (although I think I got to the final area then had to go to sleep and complete it the next day). I also played an ungodly amount of Hades in one sitting, but didn’t get the “full” ending in one day.
The Witcher 2 takes around 24 hours to complete the main story. Are you sure that you finished it in one sitting?
There was some sleeping, but at my age, playing a game over the course of one long weekend is definitely “one sitting” ;)