Here lies a long crappy post about Code Geass and its protagonist in which the point is probably not communicated very well but I'm tired and don't feel like editing it.
Code Geass R2 is almost certainly the most popular anime this year. It seems to have hit some chord with almost every category of anime fan. There are a lot of things that could be said about why it is so popular, from its generally high production value to its pretty Clamp character designs to its exciting mecha battles to its general DRAMA. Those are all a core part of its popularity, to be sure, but none of them really set it apart from many less successful shows. I want to talk about some of the problems the series has, as well as the one key thing that really makes the show interesting and fun to watch.
Basic story
Code Geass is primarily a story of two young men in a world dominated by wars in which the ever-expanding Holy Empire of Britannia has taken over much of the world. Lelouch vi Britannia is a son of the Britannian emperor, cast out to Japan along with his blind, crippled younger sister Nunnally after their mother, one of the emperor's wives, is assassinated in the palace. Suzaku Kururugi is the son of the Prime Minister of Japan and Lelouch's only friend in Japan. After Japan is invaded by Britannia, Lelouch, who already hated his father for not protecting his mother or his sister and for exiling them, vows to Suzaku that he will destroy Britannia. Years later, in an unexpected encounter with a mysterious girl named C.C. (pronounced C2), Lelouch is given a Geass, the power of kings, enabling him to give one absolute order to any person that cannot be disobeyed. Using this power along with his own strategic brilliance, Lelouch puts on a mask and becomes Zero, leader of the Black Knights fighting to free Japan, intending to destroy Britannia and create a peaceful world in which his sister can live happily. Suzaku, on the other hand, has joined the Britannian army with the intention of rising to the top and changing the world from within. And so the story begins, with the two friends on opposite sides, divided in their beliefs on how to make the world a better place and on whether or not the ends will justify the means.
Problems with the show
The show's main problems are with the plot(hacks) and the general complete bullshit. While the series doesn't go the route of Gurren-Lagann and just go all-out ridiculous because it knows it's ridiculous, it doesn't seem to worry too much about being ridiculous if it looks cool. Lelouch's "brilliant" defeats of his enemies usually take the form of "Oh look there's something there that I can blow up to take out half of the enemy army by causing a landslide!". They are often considerably more ridiculous than that, and they're generally not something where it makes sense to you as the audience that he would have known that and been able to do it. It's more like... "Wait, where did he get that SEA CHART that he's standing on the cliff with, and how is it that he used that to figure out that he could blow something up there and cause some bullshit reaction that would destroy his enemies? WTF?". It's also really hard to predict where the plot is going to go from episode to episode in general, which means it probably doesn't all tie together quite well enough. Note that season 1 is not generally considered to be so bad in this regard as R2. Finally, the ridiculous stuff he sets up by using Geass on people, while never as stupidly convoluted as the schemes Light Yagami from Death Note concocts, are still kinda stupid sometimes. Some seemingly over-specific orders conveniently come in handy later in the episode, leaving you thinking "Riiiiiiight......". And then there's Suzaku and his wall-running and breaking turret guns and spears alike with his feet, but that's another story (Spinzaku!). Oh, and the absolutely ridiculous rate of advancement in the Knightmare Frame (mecha) technology over the 2 years or so during which the series takes place... from simple ground based mechs with guns to flying mechs with huge glowing wings able to shoot blasts that take down whole armys of weaker knightmares.
Character who is both good and evil = AWESOME
While Suzaku, C.C, Nunnally and maybe Karen are all central characters, make no mistake: Code Geass is the story of Lelouch vi Britannia. Before giving Lelouch his Geass, C.C. warns him that the power of kings will bring him loneliness. Indeed, while the power to bend the minds of others with a single absolute order gives Lelouch the power he needs to fight against the world, its use leads to unexpected tragedies while the persona Lelouch has taken on as Zero must make horrible, cold-blooded decisions in order not to lose all the progress he's made in his crusade to change the world.
Lelouch's character single-handedly carries this series. And I think what's so interesting about Lelouch as a character, which makes people want to keep watching him, is that he is at the very same time a good guy AND a bad guy. And not in some lame sense where he has a split personality or he turns evil when it gets dark, though you could say that from the beginning his desire to create a world his sister can live happily in is inherently juxtaposed with his desire to destroy Britannia. Until almost the very end, only the viewer and C.C. know Lelouch's true wishes and his true intentions. He believes that the messed up state of the world cannot be fixed peacefully, and that unless someone stands up and fights against Britannia's tyranny, the world he wishes for cannot be created. Thus with good intentions he takes on the mask of Zero. As Zero, he has to be merciless and calculating to win against the vastly superior Britannian forces with the small group of rebels he gets to follow him. He has to show power and absolute confidence to keep his followers believing in him. As the rebellion he's started comes closer and closer to home, causing pain and loss for people he cares about, and as hatred toward Zero begins to grow, he realizes what he's becoming but finds that all the more he can't afford to let all he's done be for nothing.
While the audience gets to see the good side of him, the world around him only sees the evil. As the audience, you hope and pray that someone will see the good Lelouch is trying to do and that he'll gain an ally who knows who he is and understands him (besides C.C., who helps Lelouch to a degree but mostly watches seemingly without much interest). But every time that is on the verge of happening, something goes terribly wrong. It seems that it is the curse of his Geass, that will lead him to solitude. In one instance, something unexpected happens with his Geass, leading to the loss of one ally, earning Suzaku's undying hatred, and cementing Lelouch as someone who has committed an unspeakable act of evil. More and more pile up, things that no one would believe the truth about, until finally no one can trust Lelouch and he is almost universally hated. He, knowing that he can't be forgiven and can't explain his actions, must accept his role as evil to move forward, while still struggling to make things work out well.
It's easy to compare Lelouch as a main character to Light from Death Note. Both are interesting, in that we are following a bad guy as the "hero" of the show. The difference is that Light is truly, unforgivably evil and it's really not possible to root for him the way you can for Lelouch. With Lelouch, while watching his "evil" act, we get to feel good about him and what he's trying to do, even if he's a little off track. At the same time, bad guys definitely tend to be afforded huge bonuses to their "badass" stat by not being so bound by morals and not-killing-people and such as normal good guys. As part of being a bad guy, Lelouch gets to do evil laughs and kill people and bend people's minds to his will and have them kill other people, kill themselves, or any number of other things. He's incredibly badass in that sense. Geass looks really cool and evil too (GLOWING RED EYE). It's fun seeing Lelouch the evil genius defeat his enemies. It's nothing like watching a good guy defeat a bad guy.
There's really a lot more that could be said about the series and about Lelouch as a character, but I'll leave it at this. Lelouch was one of the most interesting and fun to watch characters I've seen in a long time. Oh, and given his being both a good guy and a bad guy... then ending to the series was amazingly good and appropriate.