This week's Xbox One X launch isn't just notable for the release of new hardware: it's also a bump up in quality for a lot of backward compat games. Case in point: Halo 5: Guardians.
While we're still waiting on games to get patches for the Xbox One X - it's like the PS4 Pro launch all over again - a chunk of classic Xbox titles have gotten an update for this week's launch. One of those is Halo 5, a game that we were last talking about (because it'd gotten a release of sorts on the PC).
Youtuber ElAnalistaDeBits has got a graphical breakdown of the improvements between the original Xbox One and the Xbox One X versions, and it's a good primer for what people can expect with backward compat games on the beefier console. In short: texture filtering is sharper and better at distance, textures are cleaner overall and antialiasing is improved.
This screenshot illustrates the difference in quality nicely:
ElAnalistaDeBits's full video is below. It doesn't include comparisons of loading times between the Xbox consoles, something that the Xbox One X improves in general (not just with backward compat games either).