The rulebook takes you through each phase of a turn in sequence to make the game very easy to learn. The rules are not hard to remember, mainly because there are not a large number of exceptions to the rules like in other wargames. Four hours or more is a good estimate, but it can be shorter if one side concedes (usually after the fall of a capitol).
It is very strategic. You must coordinate your limited resources with the efforts of your allies to win. You must also look a turn or two ahead when deciding what units to build for the war effort, especially when planning any large invasion/offensive.
YES IT's FUN....but it is nostalgic for many of us....4+ hours is what it would take for 2 semi experienced players. Some of my epic 5 player games lasted 6+ hours .... it isn't complex but there is a lot of pieces to move. But it creates fun memories once you get through the initial set up and shock of it.