UI: Action Buttons
One of the things that feels fundamentally wrong for me in Prime is the action buttons. Consider the following image:
When you use the Main button to attack, the position of the action shifts up. This make the action area change and, even if you don't notice it, it forces you to have that in mind when you try to use the next action. In my first days I would hit "X" accidentally because of it. I had to force my brain do adapt to something that didn't came naturally for him.
Then the biggest issue here for me: there's a reason commit buttons are usually below selection areas, This is particularly important when holding a mobile phone, As you can see in the right image, because the button is above the selection area, I lost all that information that it gives me: the current XMP level I'm using and the quantity I have, Also, it hides a part of the game area. Still today I have the need to move my finger to the side to have regular updates on this info.
Switching the Back(X) and the Action button should be the logical decision here. Also, because of visibility, LEVEL and QUANTITY should be above the XMP.
Regarding the Back/Exit button, this could be an gesture in the Action button, like "sliding down" or "sliding left".