If someone told you a 2001 Xbox game would be downgraded for the purpose of adding it to more modern and powerful devices, would you believe it possible? That is exactly what happened with Halo Combat Evolved, following a Gearbox port.
Halo Combat Evolved came out in 2001 for Xbox only. The game was so successful that is propelled both Bungie into the game development stardom and Xbox consoles to becoming proper competitors to their PlayStation counterparts throughout generations.
In 2002, Microsoft decided to release the game to PC and entrusted Gearbox Software with porting it. This turned out to be a colossal mistake in some departments, such as the graphics. Just like Late Night Gaming described in the video above, Gearbox managed to mess up both bump mapping and transparent object shaders.
Bump mapping is a way of using textures to create an illusion of depth on flat surfaces, enriching the game environments in the process. It is highly successful and is used in video game development even today.
Halo Combat Evolved used this technique heavily but Gearbox managed to mess up lighting on every level and map, resulting in an apparent erasure of bump mapping. It was actually still there, but would only work when someone shone light on it. Otherwise, the textures would appear flat. You can see the lack of bump mapping and its appearance following a flashlight activation, at 2:35 mark in the provided video
When it comes to transparent shaders, Gearbox seem to have downgraded the game through messing with one single parameter, shader_transparent_generic. It just so happened to control every possible transparent object in the game. Messing with its functions caused Halo Combat Evolved to display everything that was transparent in a much lower quality.
Instead, they dropped all the transparent objects into a less advanced shader that is responsible for the inferior visuals. You can see a direct comparison on 4:22 mark in the video.
Unfortunately, Halo Combat Evolved Anniversary and Master Chief Collection are using the Gearbox version of the game which means all those broken graphics carried over to modern day. So why would they use the version with broken graphics?
Well, Gearbox added online multiplayer support without which it would be hard to imagine Halo today. Thankfully, Saber Interactive did make the game a bit prettier with Anniversary but bump mapping and object transparency issues are still clearly visible and will likely plague MCC when it releases on PC.
In a nutshell, we are stuck with graphical issues of a botched port 16 years after it was released.