I'd love to see some sort of single-player dungeon crawler game. Exploration, level ups, power ups, equipment, combat, puzzles, etc. etc. etc. Like Wizardry as a simple first person 3D environment, or top-down like Gauntlet or Bungie's old Minotaur game (despite the fact it was essentially multiplayer only.) Interface something like single-click to move to that location, double-click to attack or otherwise interract with the environment (doors, chests, pick up stuff.) Icons to the side for health display, inventory screen, etc. Other game ideas, from olden Mac days - Bolo, the classic tank game. Mealstrom, the asteroid shooter. Solaris II, the space invader style. Crystal Quest. Lode Runner style platform game, maybe something a bit more advanced like Out Of This World.