The same can be said for just about every show, movie, game, and book these days. They're all things that have been done before thrown together in different combinations with different presentations.
I can't think of any other show that throws together a battle of the wits-type story with mechs, politics, war and strategy with a strong emphasis on strategy, and powers and mysterious stuff like the Geass and thought elevator, etc. They've all been done separately, of course, but not really thrown together in the same way that Geass is.
Also, CG likes to avoid cliches. They'll take archetypes like the pacifist princess or the broken moralfag and twist them, or make a scene that looks like a 9/10 on the "I'm dead" scale and have the character survive it. The protagonist has to battle Murphy's law every step of the way. And the main character is definitely a rarity amongst anime leads, too. He walks the line by being practical and knowing that he's going to have to cut losses to win without turning into a complete monster, and he's not the ace pilot. He uses his head and relies on his subordinates to get things done.
CG definitely has a fresh feel about it.