1.) Make the Immigration NF more useful. I haven't been able to see any useful effect from it.
2.) Allow states to be taken and made colonies. This will help fix the issue now where Oregon and Washington attract far more people than the states the USA takes from Mexico.
3.) The American Southwest should probably start as colonial states of Mexico. (Alternative to #2).
4.) Rebel Sentiments event should not probably fire for slave states taken outside of North America. I took regions from Siam and Dai Nam as USA, and they got CSA cores and called American CSA on the map.
5.) Ottomans may need a buff. With the current mobilization rules, they can't mobilize worth squat. Maybe add some accepted cultures or add some related events to add/remove Balkan cultures as accepted?
6.) Ammunition should be more prominent.
7.) Rollback the change that units use their attack or defense rating based on whether they attacked or defended, or rebalance the tech trees and artillery to compensate.
8.) Spread out the pluralism bonuses from Ideological Thought inventions to other techs in the tech tree, or add some harsher prerequisites.
9.) Supply consumption should increase for armies not standing in a friendly state (thus, increased costs to defend colonies).
10.) Cavalry should be able to be built without tech, or an Irr. Cavalry unit should be added to compensate. It seems stupid that many nations can't stick an idiot on a horse and send them somewhere, given that has been military tradition for millennia.
11.) When a nation sends you a peace offer, list the prestige or militancy hit associated with accepting. Also, call out what war goals are not being offered. Wars with lots of war goals can lead to confusing peace offers.
12.) Austria and Prussia never seem to go after each other for Hegemony wars - this seems to have unbalanced Central Europe.