Zero elevates Star Fox from an OK franchise to a great one.
In SF64 and Assault, it always bothered me how if you missed an enemy because you were focused on dodging, your chance to shoot them was gone as soon as they were to your side or past you offscreen.
In Zero, you can now dodge one way while shooting another, allowing you to shoot down enemies that are directly below you or above you, or directly to your left or right. You can even shoot down enemies that have already flown past you. And it's all thanks to the alternate perspective expanding your field of view, and your ability to aim independent of your flight.
It's not a gimmick. It's a paradigm shift tantamount to Super Mario 64 going 3D. It's amazing once you get it, which for some people happens in the first hour, and for others may take an entire playthrough. But when it clicks, it clicks.
Which could be done by using the Left Stick to maneuver and the Right Stick to control the retinal.