The Witcher 2: Assassins of Kings Enhanced Edition was released for the Xbox 360 back when the series was still exclusive to PC. The Xbox 360 version was a great port of the PC version but as it was common at that time, it was targeting native 720p resolution and had some performance issues along with screen tearing. The recent update for Witcher 2 on the Xbox One X has now made it run at a much higher resolution and also improved performance along with it.
VG Tech has conducted an analysis of the game on the Xbox One X including a frame rate test for the game running on Xbox 360, Xbox One and Xbox One X. According to their calculations, the game now runs at 3840×2016 on the Xbox One X, which is a 9x increase from the 1280×672 resolution of the Xbox 360. The horizontal resolution perfectly lines up with native 4K while the vertical resolution is slightly below it, but the game still holds up really well regardless.
The Witcher 2 renders at a native resolution of 1280×672 on Xbox 360, Xbox One and Xbox One X using the Performance Mode. The Witcher 2 renders at a native resolution of 3840×2016 on Xbox One X when using the Graphics Mode. Performance mode on Xbox One X is capped at 30fps
We have already compared the visuals of Forza Horizon on Xbox One X while the other 2 recently added games are Crackdown and Fable Anniversary. Both of these get similar enhancements with a free 4K update on the Xbox One X through backwards compatibility.