At the end of the day Far Cry 2 is a great game. The campaign will take you a good 25-30 hours to beat if you include the repetitive side quests. The Dunia Engine is a very hi-definition engine which does a lot of interesting things for Far Cry 2. There is a very good map editor. It's just a shame the online multi-player mode isn't very fun.
If you are looking for a game with immense action and a huge open world map Far Cry 2 will fulfil what you are looking for.