It would be best to go to the site itself to see the changes, but here is a snipper:
What is Vibrant Visuals?
Vibrant Visuals is a visual graphics upgrade that will transform the way players experience Minecraft. Initially releasing for Minecraft: Bedrock Edition, it is our developer’s vision for what Minecraft looks like with improved visual elements such as directional lighting, volumetric fog, and more. The result is dazzling – shadows move as the sun arcs across the sky, water reflects the landscape around it, and clouds appear infinite as they stretch far into the distance.
Vibrant Visuals brings thousands of individually crafted elements while preserving what makes Minecraft unique. Chief Creative Officer Jens Bergensten describes it as “a new look that still stays true to our creative principles”, as biomes and builds come to life with the addition of a range of graphical enhancements. But what you will notice the most is the interplay of light and shadow.
Improvements including volumetric lighting mean you’ll be able to watch the sun’s rays carve across the Overworld, and every block will cast its own shadow. Light will shine through your windows, and you’ll be able to see reflections in water and on the surface of metallic blocks, while subsurface scattering brings a gentle glow to leaves and grass. “Water is one of my favorite improvements,” said Game Art Director Jasper Boerstra. “It looks absolutely amazing.”
Mobs and items will also have more of a glow – spider’s eyes will be even more menacing in the dark, and torches will cast a radiant path back to your build. You can see this in action in the deep dark, too. “The sculk is now more emissive, more immersive, and it creates a really magical scene,” adds Jasper Boerstra.
As a cosmetic update to the game, Vibrant Visuals graphics will not impact gameplay mechanics. This means that existing lighting mechanics such as when hostile mobs may or may not burn, crop growth, daylight detectors, mob farms, and more will all still work exactly as before. This also means that players on a Realm can all play together regardless of whether or not they are using Vibrant Visuals – as the gameplay of Minecraft remains the same. As Jasper Boerstra explained in the broadcast: “Vibrant Visuals is backwards compatible with old worlds, and it runs locally – so you can play together with friends who don’t have it activated.”
The changes are coming to Bedrock first, but are coming to Java as well at a later date.
Honestly, I'm not a big fan of the current previews. In particular, the reflections feel too extreme (esspecially off the grass) and the colour feels a bit off. That said, Mojang has been shifting towards more customizability and if this is included in that, I'm sure modders and artists will do great work with the tech.