Hello Carl,
   The answer to your question is rather lengthy. I will start with a general answer and can get more detailed if you like.
1) Many units take time to build with the total cost being spread out over multiple season (turns). Armor takes two seasons to build with a cost of 3,3 instead of 6 all at once. Battleships cost 5,5,5,5 - taking a year to build with a total investment of 20.
2) Factories are not gateways for units but instead represent an investment in military production infrastructure and permanently increase your countries total production output.
3) Air units can scramble away or react to battles taking place in adjacent territories.
4) Has a 25 turn limit (based on seasons) in which victory conditions change based on historical occupations.
5) The map is produced in proportion to where the majority of the battles take place.
6) The game doesn't impose any artificial limitations on what countries can or can not do but the game is built on common sense to a large extent, trying to represent the realistic historical capabilities of each country, but offers a limitless array of approaches on how to win (again, on a very historical approach if that is what is wanted)
7) There are 2 general types of units - "Front line" and "support". If support units do not have a front line unit to "support" they are less effective.
8 ) Strategic, Rail and Tactical movement takes place all at once.
9) Out of supply rules exist.
10) There is an mechanized/armored breakthough phase.
11) Other units that A & A does not have that we have are: AT Guns, German 88s, German Stukas, paratroopers, Russian Sturmoviks, British Early War Naval Fighters, British and US Heavy Bombers, Russian Katusha Rockets, separate cruiser and destroyer units, the Japanese Yamato Battleship, Light and fleet carriers.
That is a start.
John