Code Geass is listed in the top 10 most popular Anime to ever be made, which is very impressive since there are literally thousands of Anime series on the market today. Code Geass can attribute its success to its very dark themed reveng plot, which sees the main character, Lelouch vi Britannia, starting a rebellion against the Holy Britannian Empire, in attempt to get revenge against his father for crippling and blinding his little sister, murdering his mother, and exiling them from their own country.
That isn't all there is to Code Geass, though. Code Geass is a very popular Anime amongst guys due to it's use of Mecha units (similar to giant robots that people pilot), and high amount of action used throughout the series. The series also follows 2 (possibly 3? if you could C2) romance subplots, one being his friend Shirley, who goes to school with Lelouch, and the other being one of Lelouch's own rebels, Kallen.
Lelouch, who is only in his teens, and currently attending school in Japan (after being exiled by his father), is disgusted after seeing Britannians slaughtering innocent Japanese (referred to as "Eleven's"), and comes across a strange woman named C2 who asks if he wants the power to change the world - to which Lelouch agrees to, and ends up gaining the Power of the King: Geass, which is a special power, with differing effects for each person who gets it. Lelouch happens to get the power of command, to command a person to do anything he wants, only once.
Lelouch uses this power to create the persona: Zero, which he uses to combat Britannia along with any and all other nations and forces that stand in his way, including, but not limited to, China, Europe, and even Japan itself.
The rebellious group Lelouch makes up is called The Black Knights. They fight for justice originally, trying to free the people of Japan who've been enslaved by Britannia, but eventually realizing that's pointless, and going after the entire world.
The has achieved massive popularity throughout the world, even in countries where Anime isn't incredibly popular - which is a sign of just how great the series really is. I can also say for a fact, that Code Geass, dubbed in English, has a fantastic voice cast, that adds immense emotion to every single scene, sad, funny, and epic alike.
The Anime is recommended for anyone who is interested in a dark Anime with a strong plot, not the usual Anime that are released every other day. Code Geass is one of a kind, and will always remain one of the best Anime creations of all time.

What do the anime genres mean? 

Of course you know that the Genre "Action" has action in it but, what does action in combination with say Ecchi mean for instence? it mean's (most likely), it'll be something similiar to queen's blade or Ikkitousen, now I'm not saying these series are bad or anything, they're just not my kind of anime.

I however prefer an anime like Code Geass with it's genres being, action, drama, psychological, science fiction, supernatural, mecha now let me explane these genre a bit more.

Action, what it mean's is that within the series there will be fighting for instance in code geass they use there Mecha's to fight but nevertheless there are fights. So people whom like seaing fighting should go for an anime with said genre.

Drama, all deep storylines require drama or it isn't very deep or moving I mean, real life isn't all sun shine a daises, it's all over the place, one minute everything can be fine and the next, the complete opposite so when I watch anime and it's all happy 24/7 I feel like it's a lie or that it's missing something. However what  Drama means is that the story will be sad or tear jerking or that a character within the series might die, with drama you never really know.

The Psychological genre on the other hand is often thought of as a genre like horror with blood and guts, however it is quite diffrent in fact, a Psychological anime is more about the mind and how it makes some characters act certain ways or even have emotional trauma sometimes  characters will even have deep rooted issues such as depression. An example of this is shinji form Evengelion Neon Genisis, he was depressed and at times hated himself and this made him grow as a character,  because he had to overcome his faults.

So I think, that when an anime with a Psychological genre, gives characters more of a human side, how not everyone is perfect, and that the characters have problems, not just with what's around them but more of an internal struggle which, I, always find is awesome.

Moving on, Science Fiction, now sci-fi things in general have always interested me and in code geass there are a lot of sci-fi thing within the series for one they have "Nightmares" but before I continue I'll write about Mecha here to since the sci-fi and Mecha part are basically connected.
"Nightmares" are giant robotic Machines that are piloted by people and are used for war, or just to keep people in line. Other anime that use mecha in it's genre's will also have robotic units in it's series, and they'll be called something unique to there series but it'll still be a large robotic unite with a pilot inside controlling it. It's always the same, even in hentai and manga series.
However it has more then just Nightmares it also has Flying airships with powerful weapons, but flying island castle with weapons of mass destruction, now if these things aren't sci-fi I don't know what is.

Onto Supernatural, In Code geass the supernatural element plays a large part of the series since Lelouch gains the ability Geass a special power given to him by a mysterious girl named C2 or CC if you will. if an anime has the genre Supernatural in it it'll have something to do with mystical creatures or people, which could be monster ranging from demons to vampires and even super powers.