I own the second edition, and recently got a peek at the first edition. I didn't peruse the rules for more than a few minutes or so, I did notice there weren't many changes. The map is the same. Combat seems to be the same. The first edition has more in the way of "economic" warfare than the second - you can break and repair rail lines and forage for supplies - but I think that the rules for doing so are a bit involved for a game of its level, and don't really give an idea of the difficulties that it gave the Confederacy.

The second edition has several optional advanced rules. Leaders are one of them - the CSA gets Lee (+3/+2), the Union Grant and Sherman (each +1/+2). Each leader has a time of appearance (when they get their first rating) and a time when their rating changes (Lee's moves down to reflect the death of Stonewall Jackson, Grant and Sherman go up to reflect their promotions). The rating reflects the number of die rolls that can be modified down in a combat situation by the presence of the leader (or, the leader can change a single die roll by multiple steps).

Other optional rules for the game include a table which is cross-referenced by a die roll to generate the number of marches a side can take per turn. This gives the CSA an advantage early on, but gradually the USA gains from the table. The table also can be used to allow only some units (of a stack) into combat at any time - this reflects the problem (common for the Union early on) when a general would not commit all his troops to battle for one reason or another. (Leaders help here too - the rating of a leader allows that many more troops into battle on the first turn.) There are also rules for morale effects during combat.

The second edition is a mighty good game, and I heartily recommend it.