It's mostly impressive from a technical standpoint, since the programming of games from this era would be strongly tied to the display resolution, eg. a programmer could know which background tiles or entities could be shown in the viewport at any time, and dynamically load/unload them for performance reasons. All of these optimizations now need to be tweaked or removed in the widescreen version so things outside the original 4:3 viewport don't disappear at the edge of your 16:9 display.

More recent games use flexible approaches to allow for different aspect ratios, which would behave similar to eg. fluid design on the web.

Jon Burton of TT Games has an interesting Youtube channel where he goes over some of these old school development techniques, if you wanted to learn more; eg. https://www.youtube.com/watch?v=96DO4V8qrR0 uses a lot of techniques that would be difficult to extend to a 16:9 display.

The gameplay and design heavily lean on there being a fixed aspect ratio so one would assume that expanding it would be a fairly challenging project.