The Empire of Britannia has conquered most of the world. Japan is now a province of the Empire, stripped of its name and referred to as just "Area 11". Order is enforced with powerful mechas, and all rebellion is quickly stopped.
Lelouch is a Britannian (yes, I know "Briton" would be more natural, but these are Japanese we're talking about) whose mother was murdered, and thus hates the Empire. He can't do much about it, though, being just a student, although a brilliant one.
One day, caught in the middle of a skirmish between Britannian forces and Japanese terrorists / freedom fighters, he receives a strange power from a dying girl. The girl is soon revealed (to us, if not to him) to be the result of experiments by a semi-clandestine imperial laboratory. The experiments and the lab are destroyed by their creators in a hasty damage control operation: Lelouch is now the only person with that power.
What's the power? "Just" the ability to compel anyone to do his bidding (once, he'll learn soon enough).
With this power, his great intellect, and some kind of support from the freedom fighters, he vows to destroy the Empire and rebuild a world in which he and his sister can live in peace.
This could be one of the great anime of all time, and it is very good, but its flaws prevent it from reaching greatness. Let's start from what I didn't like.
Most of the characters are schoolboys and schoolgirls, hiding their identities from each other; this set-up is much more fitting a comedy than a war story, and sometimes it shows.
There's some filler material, which gets irritating when you realise that the story is not going to be concluded in these 25 episodes.
Lelouch's quest to find who killed his mother feels a bit repetitive, hunting down the main suspect only to discover that it was not them, and they have very little information on the matter.
What did I like?
Clamp's character design, which I usually don't like, works rather well: the angular faces suit the serious and very determined characters.
Lelouch: he's terribly smart, and his efforts to balance his multiple goals (avenge his mother, safeguard his sister, help the rebels, topple the Empire…) make for a very complex and interesting character.
In fact, most of the characters are well developed and have some depth to them, they're not just background for Lelouch grand plan.
The story, even with the limitations described above, is engaging and appropriately filled with twists.
So, if you like smart characters engaged in complicated plots to change the world, and prefer mecha battles to shinigami, this is quite probably a series you should watch.
Curiosity note: the "Geass" in the title is probably a mis-spelling of the Irish "geas" or "geis".
