I remember reading at one point that the developers of BL2 were trying to one up BL1 by increasing the number of kill or stack skills which appear on screen while playing. I can not find the article but they were so proud of this achievement. I do agree that it is so great to see all those hexes appear in BL2 and they did a mostly great job at indicating to us these skills in the trees.
I preface this that I have not played BL3 yet at any of the venues, I am basing this suggestion on my obsessive digestion of gameplay videos.
I feel that BL3 has taken a step back in with respect to kill/stack skills that now appear under the XP bar. I do not mind the placement, in fact I think it really works. But the skills are hex shaped which clearly indicates an active skill from the trees. Also, I really think they missed an opportunity to color them by their tree. In a recent interview with Chris Brock, he mentions encouraging the players to share their points across several trees. Well it would highly benefit us if these kill/stack or skills for whatever active conditions are better represented both in the trees as well as on our HUD. Color coding would a great first step to encouraging this. A different shape or star or something in the tree would be highly desired.
In addition, while I know all other factions of the game seem stellar, I do feel the HUD has not improved over BL2. No longer do we see what type of ammo we pick up. No longer do we see our shield or grenade mod though this is understandable given the multiple perks these mods have now. And above all, why are the key bindings not shown for exiting, switching seats, or firing when you are in a vehicle like they are with skills? Do you know how many people in videos switch seats instead of exiting a vehicle because the keys are not on the screen? These small changes lead me to think that the HUD has not gone through the same consistency quality assurance that the rest of the game has likely experienced.
Most of the people are thinking these are such small things. I agree, they probably will not change my enjoyment of the game. But we will be watching the HUD more than anything in the game. It would have been nice to know the small things could have made it that much better.