Coming in as more of a painter than a photographer, I have a slightly different series of features I'd like in the program.
First, and probably most importantly, is the ability to have instantaneous response from the color picker rather than having to click and drag to select a color
Second, is being able to clip layers (or even groups) to a group
Third is to be able to bind macros to hotkeys
Fourth is to be able to transform respective to an arbitrary point, rather than just the centre of the selection or its edges/corners
All of these are features I use frequently in Photoshop, and are the main things preventing me from completely jumping ship