Iron man mode is the traditional roguelike mode i.e. if you character dies you have lost and your save file is automatically erased - no second chances! Normal mode is more forgiving; it allows you to indefinetly restart the game from the last save point. Save points are automatically created everytime you leave an area. Keep in mind that the game is balanced for normal mode i.e. iron man is damn hard/unfair. Your score is modified according to this i.e. iron man players get more points than normal players.