It has a lot of Mechas, this is how open warfare is done in this show. However, the drama, character development, and the plot all take the spotlight and drive the anime more than the action (which is also very good).
It is about a corrupt Government who has taken control of the world and oppresses the minority through their power. The main character happens upon someone that could give him the ability to start a revolution, and create a world that he deems fit and safe for his little sister. Main themes of the anime are : Fate vs Free Will and "right" vs "wrong." There are others, but these seem to be the most developed.
I typically don't like mechs, but Code Geass is my favorite anime. Even if you don't like mechs, I STRONGLY recommend you check out Code Geass =D