An animated show of French origin that used to air on Cartoon Network.

Code Lyoko is about a bunch of kids who live at a boarding school and discover an incredibly advanced supercomputer hidden in an old factory. They turn it on and end up unleashing XANA, a rogue computer program that is able to project itself into the real world and cause all kinds of destruction, usually by taking control of things such as animals, machinery and later people.

The computer also houses some kind of virtual world, which our protagonists can enter by stepping into these cylindrical chambers called "Scanners" which turn them into data and transport them into the computer. The show uses a combination of hand-drawn animation for the real world, and CG for the virtual world.

They could shut down the computer and be rid of all this trouble, but there's one problem, and it's name is Aelita. An elf-looking pink haired girl who lives inside the computer, whom the resident super-nerd of the group ends up being smitten with, so he and his friends decide that they're going to fight Xana until he can devise a way to bring her out into the real world.

Xana causes problems by activating these odd glowy pillars on the virtual world called Towers, which allow him to project into the real world. The only way to stop his rampage of the day is for our heroes to fight the virtual monsters he uses to guard the towers, and have Aelita enter one and de-activate it. 

Another peculiar feature the Supercomputer has is the ability to "return to the past", which seems to cloak the entire planet in digital data and rewind it to an earlier point. Time travel basically. It is said that this cannot revive someone who has died, so there's still plenty of urgency in fighting Xana.

When fighting in the virtual world, our heroes have a system of HP that the show doesn't really keep track of. When they lose all of these life points, they get ejected back to the real world. Aelita on the other hand will permanently die if all of her life points run out, so there's a great urgency to protect her.

The first season was structured in a very simple (attack of the day) formula that can be watched in any order. The basic formula went like this.

-Our heroes deal with a real world conflict (like a snobby girl blackmailing one of them) until a Xana attack happens in the real world.
-Some of the characters go to the virtual world, others stay behind to try to deal with Xana's attack in the real world.
-Aelita (who has zero fighting power) runs around making a near orgasmic panting noises as she's being chased by monsters. She tends to try to do things on her own and sometimes it works, sometimes it causes trouble.
-Our heroes arrive and save her bacon, or sometimes she uses her cleverness to do it herself.
-Meanwhile certain doom is happening in the real world, like a character is seconds away from death.
-Aelita deactivates the tower and "Return to the Past NOW!"
-The earlier real-world conflict gets solved.

Only at the end of the first season do our heroes manage to bring Aelita into the real world, only to discover that she's still linked to the computer and will go into a coma if it's shut down.

Season two however gets a little deeper, delving into the origins of Aelita, the super computer and Xana. The basic formula is still there, but it's spiced up by actually having character development, and the introduction of a newcomer to serve as a romantic rival between two of the main characters.

Season two also gives Xana a bit more plot and motive as well. In the first season Xana was basically a mindless creature of destruction, and would not hesitate to shoot Aelita down will full force. In season 2 he's much more strategic, and needs Aelita alive for plot related reasons.

The show initially ended with the fourth season, but was recently brought back with a sequel series called Code Lyoko Evolution. It's........ controversial. The biggest issue is that the hand-drawn animation segments have now been replaced with live action, and our cast of twelve year olds is played by people in their 20s.

Another problem is that the switch to live action limits the scope of what Xana can do. Xana's attacks come in very creative forms. One episode involved a Xana attack coming in the form of a snowstorm that would make Elsa's powers look like a pleasant Christmas. Another involved him taking control of a pack of wolves.

With the show switching to live action, stuff like that doesn't happen. They usually just get a human to play the shape-shifting ghosts Xana can create in the old series as well. One episode involved Xana taking the form of a little girl, who attacks people by trapping them in a HUG, and they can easily push her away. 

There are so many reasons why this is ridiculous, but the big one is that Xana's specters tend to have super-human abilities. They can jump rooftops, walk on walls, pass through walls, you name it. Obviously we're not gonna see that in live action.

One thing that people remember the TV series for was the complete lack of a radar the show had. Apparently it's the result of the show being produced and even dubbed by a French studio, where things like young girls being shown in their underwear isn't as big a thing as in America.

Wow this got way longer than I expected. I'm done now. XD Not even gonna discuss the third and fourth season since they're not as good and they involve plot details from the second.

I marathoned Code Lyoko for the first time ever last March during spring break and then watched Evolution as it was subbed. Loved the original and enjoyed the live action to an extent. 

I love the original series because Xana was a pretty well developed villain for a kid's show. I'm trying to think of all the cartoons I watched as a kid and cartoons I watch now (excluding anime), but none of them had villains that I actually felt were dangerous (though Danny Phantom gets points for having an episode dedicated to an evil future self that tried to kill everyone Danny loved, plus Mr. Lancer). It was refreshing to see the heroes constantly scrambling and being put in life-threatening situations basically every episode. Plus, the warriors understood and respected how dangerous Xana was. Xana and the nicely written side characters made up for problems like heavily recycled animation and awkward dubbing.

I enjoyed Evolution. I can't tell if it was because I was still excited by the series in general or if I actually liked it as its own thing. I'm assuming the latter because I have more complaints about it than things I like, but... I don't know.. I'd defend it if some random person came up to me and told me it sucked and looked stupid without actually watching it. 

The live action had some really nice Lyoko scenes. They fit the spirit of the original series, even if there are a few continuity issues and the Forest and Ice sectors were gone. It was a little annoying to have Aelita go from the only person who can deactivate towers to all of the original warriors being able to, but it wasn't terrible. 

You pinpointed the biggest problem with the live action scenes perfectly. The decline of Xana's threat as a villain from life-threatening attacks to basically a bunch of specters hugging/grabbing the group to leech codes was painful to watch. It also made episode 25 feel like it came out out of nowhere. 

Other problems include poor writing choices and the lack of every character from the original series other than the warriors, Jim, Sissi, and a badly cast Mrs. Hertz and Mr. Delmas. And Sam... which is debatable given her different last name, casting choice, and personality.

On another note, I'm not really into the fandom (on Tumblr anyway; havently really looked at any forums). I enjoy fanart and fanfics, but there are too many random spouts of drama in too short an amount of time. I once took a break from the tag when they were fighting and came back to see a different fight in progress. Plus, any fandom that rips someone apart for torrenting the original series while simultaneously watching fansubs of the new series falls under fandoms I typically avoid.

I'm not interested in this, but my sister and her friend really enjoy it....

I loved this!

I watched Code Lyoko when it was on Cartoon Network block Migoozi or however you spell it. It was a girl who went under water to watch cartoons. I enjoyed it as a kid. I don't know if I would go back to watching it.

I also watched a few random episodes of Code Lyoko back when I had and watched Cartoon Network.  I enjoyed the backgrounds and general explanations of the plot and what the characters do that RLinksoul provided in the first post of this topic.  I can now see why I was interested in it back then, and I think I would enjoy getting back into it now - at least the first two seasons.  From there, I'd play it by ear (is that the correct saying?) when deciding whether to continue.

Miakemi wrote:

Other problems include poor writing choices and the lack of every character from the original series other than the warriors, Jim, Sissi, and a badly cast Mrs. Hertz and Mr. Delmas. And Sam... which is debatable given her different last name, casting choice, and personality.

I was looking into Code Lyoko Evolution, reading the TV Tropes page for it and I found out the deal with the character of Laura. I don't know whether it's hilarious or kind of appalling.

So many things wrong with this character's writing. I get the idea that they wanted a character who could have things explained to them for the sake of the audience, but good lord. Having this character who has never even touched the super computer inexplicably be able to do things that Jeremie and Aelita can't, and then gloat about how a child could do it. Wow.

Not to mention her inclusion in the group seems to have been even more grudging than William's, as she basically hijacks herself into the group like a bad fan character and they only keep her around because they have no choice.

Then, instead of having her grow on the team and prove her worth as a member, the described "unreliable" character screws up for the last time and Jeremie manages to wipe her memory and eject her from the group. Wow.

Let's not forget all the times that Jeremie has endangered the lives of others for one thing or other. Heck, the entire show was founded on him putting the world in danger because he fell in love with a computer program.