Graphics:
My wish: Make the political map very clearly defined with bright colours. A useful tool for checking exactly what is going on. Old HOI did this well, and Rome is actually better as well.
Additional long term: add an "iconic terrain map" for easy reference for terrain. With the colours of the terrain and icons being so "watercolour" (for lack of a better word) things are quite confusing as it is now and the terrain you are manouvering in is very difficult to figure out. The addition of an "abstracted" terrain map will be another helpful quick reference tool.
Even better, make it possible to use an "abstracted map set" that can be toggled on or off in options. The player would have an optional set of maps other than the standard terrain map for terrain, region, supply, VP's and intelligence, etc. Somewhere half way between HOI II and HOI III would be sufficient: Brighter; darker; richer colours.
It is particularly difficult on small screens.
Think of it like the difference between counters and sprites, except instead for the maps. One is abstract the other is representational.
Last but not least, and fairly easy to do I imagine, make the highlights for each HQ command group thicker and brighter with colours that stand out more against the map, for ease of play.