I would like to see a MUCH better user interface. I left a lenghty rant in the "Eu4" thread about it.
Don't make us have to hover the mouse over stuff or click on things to learn the relevant stats.
Make the default map mode SPEAK to us!! Make it tell us important stuff... COT trade strength, my own trade levels, tax income, revolt risk, strength of fleets in port, core province or not, fortress and blockade strengths. All of that could be put into the default map mode without make it cluttered. Have it simply appear step by step when you zoom in. Learn from the way the Civ series puts tons of info on their UI.
Don't make us have to hover the mouse over stuff or click on things to learn the relevant stats.