Four years after Celestial Being's disastrous showdown with the Earth military, most of humanity is united under a single government: the Earth Sphere Federation. A-LAWS, an autonomous task force established in the name of preserving peace and security, is in reality responsible for the brutal and oppressive enforcement of the Federation government's will. The remnants of Celestial Being notice that the world is no better off in the wake of their actions four years ago, and in fact is largely worse. Feeling the need to take responsibility for their past actions and set things right, Setsuna and the rest of Celestial Being begin re-organizing, preparing to intervene in world affairs once again.
Area 11 is still under Britannian rule and the Elevens remain brutally oppressed; what’s more, their saviour, Zero, is nowhere to be found and all of Britannia believes the rebellion is finally over. Elsewhere, having lost the battle, Lelouch sets his sights upon winning the war – but the task is no easier since the Britannian forces have learned some valuable lessons all of their own. Not only have they discovered his identity and captured many of his Black Knights, but they now manipulate the memories of all of his friends. Worst of all, they have taken the most precious thing in his life – his dear sister, Nunnally. With his hatred for the Britannians stronger than ever before, Lelouch must now recuperate his forces and bring their rule of terror to an end.
These shows have several similar aspects like rebel forces fighting for freedom against large oppressing forces (Brittannia/A-LAWS), over-the-top battle scenes with a few far superior mechas being able to fight againsta large number of enemies on it's own and characters with beyond human capabilities.
Gundam 00 and Code Geass R2 have much in common. The storyline of both series is similar yet spectacular in their own ways. Both involve a group of people trying to change the world and rid it from oppression yet they both do so in their own unique ways. The only difference between them would be that Gundam 00 expands to space while Code Geass remains on earth.
Simon lives a boring life in the underground village of Jeeha, where his main job day in and day out is to dig tunnels. His close friend Kamina, however, longs to bust out of their oppressive existence and reach the surface world where open skies and adventure await! One day, during his usual digs, Simon discovers a robot with a big face buried amongst the rocks. No sooner has he shown Kamina his mysterious find when two beings from the surface crash land into Jeeha Village - one is a gun-toting woman calling herself Yoko and the other is a terrifying mecha piloted by a Beastman! Seeing their chance to escape village drudgery, Kamina rallies Simon and Yoko to defeat the invader using their new robot, Lagann. However, upon breaking out onto the surface world, Simon, Kamina, and Yoko encounter enemies more powerful than they could have envisioned. Their fight for adventure just turned into a war for the survival of the human race - will their lust for freedom hold out against such terrible odds?
Even though Gurren Lagann is set in an more unrealistic world, both are focussed on bringing freedom to mankind.
Both series have great actionpumping mech-combat and transformations as well as huge battles with enormous fleets waging war.
Still Gundam 00 falls more into the serious/political war genre, whereas Gurren Lagann is more of Comedy and Fantasy.
If you liked the huge wars and fast mech-fights in one you'll definitely like the other.
Both shows are very different, but the main theme of fighting for human freedom stays the same. And the mecha battles in both shows are over-the-top although TTGL uses it's fights in a much more comical way than Gundam 00 which stays serious.