Shouldn't the protagonists of Code Lyoko all need therapy? I mean, think about the stress of having to save the world every day. Imagine having all your friends constantly almost die. It's amazing how resilient cartoon children are.
But the first thing I'd like to point out, in response to a lot of the comments here, that all animation does not have to look like Japanese anime. Really, it doesn't. It's not like all anime series look that great. Sure, Paranoia Agent or Cowboy Bebop are swell, but Pokemon is nothing to write home about. The French have made some very nice looking cartoons, like Fantastic Planet and Kaena. There are a lot of animators in France, in fact, and they have a perfect right to follow the French tradition of animation rather than the Japanese one. Of course, Code Lyoko is influenced by the Japanese, like most animation, but it is also in keeping with its countries products.
Personally, I really like the show's character design. It's one of the reasons I decided to check it out after seeing a commercial. A lot of cartoons look like a lot of other cartoons, and the distinctive faces attracted me to Lyoko and made me think it might be more than just another cookie cutter cartoon.
Lyoko is a rather odd show, because each episode is structured in almost exactly the same way. The evil computer virus accesses the real world, the heroes go into the virtual world and kill some monsters, and everything is fixed and time is reset to before the disaster (I haven't seen the early episodes so I don't know if they explain why or how time is reset; this show doesn't seem that interested in details).
Lyoko is definitely a kid's cartoon, even though I enjoy it. It's not as sophisticated as Batman or Trigun, but characters are distinct, there are some interesting ideas, and it does have a nice look to it. It's not a great cartoon series, but it's a good one.