A game controlled with a Matrix-style total neural interface. Though, aside from just the hardware, my "ideal game" concept pretty much already exists in the most recent Fallout games; an open-world FPS/RPG with tons of choice (both in terms of character customization and moral choice), a sci-fi setting, interesting characters to meet, and an intriguing plotline to uncover. But, of course, the perfect concept doesn't mean perfect execution, especially on something as limiting as today's gaming systems (anything that involves buttons instead of jacking my brain straight into a computer is inherently too limiting for this concept to really come int its own).