Besides better LOD management when flying and some minor lightning improvements, I'm finding it hard to imagine how much better it could possibly look compared to the base game on PS5.
I'm currently playing it and nearing the end, I think, and I've never seen a better looking game. This is the game I've used photomode the most ever. Nothing comes close. Every frame looks a straight up work of art. The lighting, the textures, the effects, the animations... Oh my god. I've even thought that "this is too much" sometimes, because I get lost in the amount of detail, movement and colour. If games from now on look just like that forever, I'd be perfectly fine and continuously amazed for the rest of my life with games' graphics. But if they somehow can make it look even better, I'll find a way to be even more amazed.
I'm having so much fun playing the game too (in hard mode from the start). The combat is quick and weighty. Exploring is always rewarding, finding new quests and people (the ones in plainsong were so touching), stumbling into cauldrons, tallnecks, ruins (with each it's own puzzle), the mounts (and it's combat is surprisingly good), stealth with traps and correct weapons and outfits is deadly. The story and the lore are so creative and makes so much sense. The character growth (specially Aloy)
I could go on and on about how much I love this game.