Coming from DOS2 I'm familiar with hotbar UI being used in this game. I generally like it but with a few tweaks I think it's functionality could be greatly improved.
1. Add keybindings for switching between hotbars. I'd suggest something like Ctrl-1 => hotbar1, Ctrl-2 => hotbar2, etc. Having to click on a little 10x10 pixel scroll arrow to switch hotbars is a PITA.
2. Have hotbars organized by type: hotbar1 => Spells, hotbar2 => Scrolls, hotbar3 => Potions, hotbar4 => Arrows. When new items are picked up they are automatically added to the appropriate hotbar.
When I'm in the middle of a battle it should be easy to determine what things I have at my disposal. I don't want to go digging around my inventory to see what scrolls or potions I have but forgot to add to my hotbar. The game should do that for me automatically. Otherwise it distracts from the game play and role playing. These two small improvements would go a long towards helping with that.
