The Xbox 360 controller, as an example, has thirteen different user inputs. That's not including the Start, Back, or Xbox buttons, and that's counting the D-Pad as one input instead of four. So with a slightly more generous definition of "user inputs," we get a count of nineteen.
This is why the Wii is the dominant console of this generation. Our games really are fun, but unless you feel like mastering a dozen-plus inputs - including, in many games, dual-analog joysticks requiring a seemingly ambidextrous mastery of independently controlled facing and movement - you're never going to experience all this great fun.
So screw that. Let's make a typical current-gen FPS work on an Atari 2600 joystick that has only one analog stick and one button. I'm going to use Far Cry 2 as our example. That game's controller diagram features the following list of inputs:
Left Joystick: Move
Left Joystick Click: Sprint
Right Joystick: Aim/Look
Right Joystick Click: Switch Throwable
A Button: Jump
B Button: Crouch
X Button: Reload/Unjam
Y Button: Interact
Left Shoulder Button: Heal
Right Shoulder Button: Grenade/Molotov
Left Trigger: Iron Sights
Right Trigger: Fire Weapon
Start Button: Notebook
Back Button: Map/Phone
D-Pad Up: Switch to Machete
D-Pad Left: Switch to Primary Weapon
D-Pad Right: Switch to Secondary Weapon
D-Pad Down: Switch to Special Item
That's eighteen different inputs. When you get in a vehicle, you switch over to a different set of thirteen inputs, for a grand total of thirty-one.
Must we use every input mechanism on the controller? What if all we had was one analog stick and a single button, like the famous black joystick of the Atari 2600 console? Could we possibly cope? I bet we could. The game wouldn't be the same but it might, shockingly, still sound like fun. Let's find out, in what I'll call Far Cry 2600.
Movement: With just one stick controlling facing and movement, we have to make a big change here. I'll just come out and say it: Far Cry 2600 will control like Doom without strafing. You can turn left and right, you can go forward, and you can go backward. You can't look or aim up or down. To compensate for this, we'll do what Doom did: if there are enemies above or below your aim point, and none actually on your aim point, we automatically target the nearest enemy above or below.
How radical a change is that? It's pretty substantial, to be sure. But Far Cry 2 isn't especially about verticality. The terrain tends to be pretty flat. You certainly use the up/down functionality to make precise shots, but our Doom-style auto-aim will do that job too. As long as the target is at least partially exposed and your aim point is aligned with their position on the left-right axis, you'll make the shot.
Different? Yep. Completely awful and unplayable? Nope, just old-school.