In order of priority
1. Fewer surfaces. They're fine, but they shouldn't be the main point of D&D combat.
2. Less barrel-throwing. This isn't Donkey Kong.
3. Disengage as an action, jump as part of movement
4. Fix the spells that are different from 5E for no reason
5. Add in hit dice and increase the limit on short rests to 3 or 4; remove teleport-to-camp from dungeons
6. Different ranges for ranged weapons (longer for the longbow!)
7. Rebalance the ranger companions so Spider isn't the only reasonable choice
8. Leave a highlight when a hidden thing is found.
9. Fix the broken quests
11. More options and more agency in cutscene dialogs (god-like snake insta-kill, I'm looklng at you) so it feels less like a railroad
12. Make it feel like time passes (burning corpses still just there burning days later?). Make the dialogs more responsive to what's actually happened.
13. Make a "loot" action pick up from all the boxes, barrels, or corpses
14. Highlight only interesting things, and highlight all the interesting things. Playing on Stadia, I couldn't find the windmill controls because the compression made them too blurry. Don't make me "Where's Waldo" for the plot.
15. More subclasses, more spells, more feats
16. More classes
17. More gear
And, while I don't think this is possible in the first area, in subsequent chapters I'd like to see less packed maps with every battle a set-piece. I love the clever set-piece battles, but there should be a wider area and that should leave room for several easy encounters between each hard one.
