The first thing you will notice it the map

. It's big and beautiful. If you remember in AACW always skirting along the far western edge of the map to sneak into Fort Smith or on to Tuscon, now the map includes ALL of Texas, Eastern the New Mexico and Colorado with Denver, and goes north to the Canadian boarder and includes most of the Saint Lawrence River in the East, including Montreal and Quebec, for those exciting occasions of Foreign intervention. If you ever get a chance to play that, it's a whole new game.
Nearly all the rules are the same, so if you've played AACW you can really just jump in and play Civil War II. One thing you will notice is that when you buy units you can now select
where they will be built within the constraints of their home states and some restrictions for building artillery and ironclads, etc. Never again will you have fat brigades building in secluded locations in the middle of winter with not enough supplies to support them during their training so that they starve before completion and hardly have a chance of moving them away before spring thaws.
Regional Decision Cards (RGD's) are a completely new aspect of the game. They allow for doing some minor actions, such as building stockades (small forts historically found in the Far West), improving the civilization level of a region (allows easier movement through it) clearing trails and even building some roads; things that can have an impact on the Far Western campaigns. You can even deploy torpedoes and the CSS Hunley! or detonated explosives under a besieged fortification to cause a breach
Great improvements have been made in the retreat rules. You will hardly ever see stacks retreat away from your own lines again, but it will also behoove you to maintain a path of retreat, otherwise your stack may not be able to retreat after battle at all; far more realistic than ever before.
New leaders--especially naval (on both sides)--and a hand full of new historical units add more flavor to the game, but 95% of the mix has remained in its old tried-and-true form so that balance has not been impacted.
So if you're interested in playing the Civil War in a game again, CW2 is definitely the way to do, especially if you're getting a Lovers of the Civil War Saint Valentine's Day discount
