5 things I'd like to see improved (listed by importance to me):
1- UI improvement: 10 ability slots instead of 8. 8 is not enough, and I keep forgetting to change them before combat. Even then, it's immersion breaking to have to go into each characters ability screen and select the 8 that you think you will use. If I have 10 abilities, I want to have access to 10 abilities during combat.
2- Better tactics screen/options. I loved the DAO tactic screens and the hundreds of options. I spent hours juggling the options to get just the right combination. I also know not everyone loved it, and some tactics were somewhat obscure. We'll never go back to that I know, but something more involved than what we have now.
3- A hold command that actually works in combat. I ran into a puzzle recently that basically required that I separate my party and have them hold certain positions. I was so shocked that it really worked. But it still is useless in combat. There are times I'd like to set up ambushes or make a stand in an archway/doorway, but it just won't work that way.
4-Tool tip overlays for skills, I agree.
5- UI improvement: 4 potion/tonic/grenade slots.