El gamepad se accede con:

Gamepad.current

Botones

if (Gamepad.current.buttonSouth.wasPressedThisFrame)
{
    Saltar();
}

Botones comunes:

buttonSouth
buttonNorth
buttonEast
buttonWest
leftShoulder
rightShoulder
startButton
selectButton

Sticks

Stick izquierdo:

Vector2 movimiento = Gamepad.current.leftStick.ReadValue();

Stick derecho:

Vector2 camara = Gamepad.current.rightStick.ReadValue();

Triggers

float izquierdo = Gamepad.current.leftTrigger.ReadValue();
float derecho = Gamepad.current.rightTrigger.ReadValue();

D-Pad

Vector2 dpad = Gamepad.current.dpad.ReadValue();

Comprobar existencia