I've been playing the game very little, but here are my first impressions and suggestions on the UI.
-It took me forever to figure how to ready your weapon
-It took me forever to figure how to load your weapon
-It took even longer to figure how to use special attacks. :-)
Few suggestions:
-Set R to reload currently equipped weapon with the first available ammo on your inventory
-Open the special abilities window when you click on empty quick slot
-Equip a weapon when you double click it
-Allow reload by dragging the ammo on weapon
-When right clicking ammo in inventory, apply it to current weapon
-Show different attack modes when pressing ctrl or right clicking the target