Some of my very fondest gaming memories took place on the Nintendo 64, but now over 150 games have received AI-enhanced HD texture packs including Duke Nukem 64, Mario Kart 64, and many others.
The folks over at Gaming Revived have, well, revived some classic Nintendo 64 games using TopazGigaPixel in order to upscale the original textures of classic Nintendo 64 games. It's not perfect, with some parts of the game and textures looking worse in some cases, while other parts look much better -- including the UI in some of the games looking much better.
Most of the AI-enhanced HD texture packs for the Nintendo 64 games are around 1-2GB a pop, which isn't too bad at all. The HD texture packs work with RetroArch using Mupen64-Next "Core" and its most recent release, but they also work with Project64 as well as Mupen64plus through GlideN64 3.0 or GlideN64 4.0. Grab the AI-enhanced HD texture packs here.
Some of these games bring back some serious memories, with the AI-enhanced HD texture packs improving the graphics (at least for the most part) in games like Mario Kart 64, Duke Nukem 64, Perfect Dark, PilotWings 64, Quake64, and many others.