Is this an improvement over the current button layout? Need opinions.

If you plan to add more skills, talents etc in the future, this will be a lot more slim eventually. Call it future proof!
I think you'll want to add a slightly visible border between the normal buttons, the shift buttons and the control buttons though.

looks good to me, but the keyboard shortcuts might get a little confusing that way. perhaps allow switching between old and new interfaces?

If you do go and add more skills through a tree system, maybe eve halving the size of the buttons, so you can add a second stack but this would be so much better.