The '4X' refers to 'eXploring, eXpanding, eXploiting, and eXterminating,' to which Imperia adds 'eXisting.' Why? Well, in Imperia players assume the role of a young intergalactic emperor who not only carries the full weight of humanity on his shoulders but also must deal with some personal issues of his own.
Usually in this genre it's the player who controls a omniscient being who can do virtually anything. In Imperia, however, your main character has a limited number of administration points that he'll need to use wisely. Misdirecting your empire will not just destroy it, but might also mean that your character gets assassinated.
Political machinations aside, Imperia players will have to manage entire planets. Their inhabitants' wellbeing, technology, agriculture, and culture... all of this depends on the decisions you make.
Imperia is a turn-based strategy game with huge potential, and despite having somewhat crude graphics, it has an original concept that really brings something new to the table.