The haptics in this pad don't let you feel shapes or elevation, so you won't feel like you're thumbing over a button. Rather, the haptic feedback lets you feel
motion. It makes the pads themselves feel like they are moving in a specific direction. It's why so many compare the right pad to a trackball - because when you flick your thumb over it, you would swear you are spinning a trackball. It's really hard to explain until you try it, but I had to spend a good 10 minutes convincing one of my friends (who doesn't play many games) that the pad in the prototype wasn't actually spinning, and that it was a flat, motionless piece of plastic, and everything he was feeling was basically his brain tricking him.
So with that in mind, with regards to the left pad, the haptics don't let you feel the d-pad. Rather, they let you feel the left pad itself shift around. You know how, on a SNES controller, you couldn't press the left and right arrows at the same time? When you would shift your thumb from the right side of the pad to the left side of the pad, you could feel the plastic that made up the dpad pivot? It basically rocked in place because it was actually pivoting on a small chunk of plastic in the center of the d-pad:
The touchpads on the steam controller don't actually move at all (other than being able to depress them down). Haptics let you regain the feeling that the pad is rocking around, even though it isn't. The physical indention on the pad is what you are supposed to feel to make you feel like you are touching an actual d-pad (and the right pad lacks this), while the physical button that the touchpad itself resides on is what gives you the weighty throw you feel when you press down on a d-pad on a conventional controller.
You can certainly use the right pad like a diamond button layout, but that's not really how the controller is supposed to be used. You have 10 separate inputs around the controller that your fingers naturally rest on without ever taking your thumbs off both touch pads. Those are where you are supposed to handle your action button inputs. If that's too daunting for you, there is an actual diamond button cluster in the bottom left corner. I think they've done a nice job of providing alternatives and redundancy around the controller, which is good design.