I finished only one game until now. We almost finished a second one. We used to play every Sunday for 5-8 hours and it still took us about two months. Very addictive game if you take the initial time to learn how to play. Kind of hard to get off though. We all got late to work a few times because we couldn't let go. Be careful! :)
By the way, you can learn about the game in other modes, but the fun game is the story mode. Yes, the story mode is multiplayer.