When I first heard about the PS4's controller including a touchpad, I couldn't help but think "novelty at best." But as there have been some heated discussions about it as of late, I've decided that the touchpad will be the best thing to happen gaming controllers since the dual analog stick.
Why? Simple: A touchpad can easily act as an additional 10 buttons. Using gestures, a touchpad will easily recognize left, right, down, up, and a regular motionless "press." And it should easily distinguish between making these gestures on the left side and the right. What we end up with is 10 comfortable and easy to pull off thumb movements that effectively adds 8 new buttons to the controller (for now let's assume that the touchpad has replaced start and select, so pressing on either side will act as these buttons. Some mockups still include these buttons as the bottom of the pad, so we may effectively get the full 10 new buttons). I did some tests on both a 360 and PS3 controller to see how comfortable such a thing would actually be. Surprisingly, it was even more comfortable and intuitive than I had imagined. (Side note: It felt even more natural on the 360 controller. Shhh, don't tell anyone!)
But what use is so many buttons, especially since the nature of gestures acts like a quick press and release (in other words, you can't "hold down" a left swipe, but you can stop your finger which could work in much the same way). The answer is simple: Quick Selections. Today, almost every action game uses the D-Pad to allow you to map up to for weapon or abilities for quick selection. This is abysmal when compared to a mouse and keyboard, which usually gives you the 0-9 keys for more than twice the number of selections. But with the touchpad and gestures, suddenly as many as 14 quick selections become possible (when including the d-pad)! Having to go through menus to select my fifth most-used weapon has always been an annoying pain, and the PS4 controller may just be the answer to those woes.
Of course, quick selection is only the tip of the iceberg. These same gestures can pop a potion or open the game's menu onto a given screen, much like the select button is often used today.
In a few short days, the PS4 touchpad has gone from useless gimmick to complete game-changer in my mind, and it has become the feature that I most desire of the next console generation.