Donkey Kong 64. Oh man that game really hasn't aged well. I like the levels and the music but man if there is one thing about that game that I want to see if it ever gets a remake is to improve the Kong Switching. Also make the collectables not so tedious to collect. Especially the ones that are required to beat the story.
Elite Beat Agents, but it will never happen. It's a rhythm game that uses covers of old copyrighted pop, punk, and rock songs that probably can't be rereleased in a new game. The game was also purposefully made with the DS' two screens in mind at the same time and I have no idea how they could translate that to one screen on a modern device. I just loved the game so much when I was younger and I wish it could get new life instead of being stuck on original DS forever.