Civilization IV makes my life complete by helping me to understand the dynamics of the world.
Every aspect of Civilization IV is clearly based on our reality - The dynamics of the technologies, religions, wars, and leaders.
It makes the world make sense through its complexity, and my willingness to learn to play the higher difficulties has caused my ability for out of the box thinking to increase drastically.
The strategic elements are absolutely incredible - How many angles can I approach a single problem with is always important to me.
Playing the game helps me to see things for what they are in the real world - It makes the dynamics of understanding human behavior much easier, and much more logical.
When I see the way the AI reacts to my actions, it always reminds me that any action I take, as in real life, will always influence those I am connected to. It makes me carefully consider the consequences of the things that I do.
There's also the aspect of the totally realistic viewpoint that you can't always get what you want - Nothing's ever fair, but if you do your best to excel it's almost always possible to come to the top!
I think that ultimately, this game has helped me get out of the "I can't do this" attitude. Now I believe "I can do this, all I have to do is try." This is the basis of advancement on all levels of humanity, and it's a component of the game that most people don't realize is there - the component of self-limitation that evolves into self-realization and understanding.
Civ IV is the best game ever, period.