One of the smarter and original anime series' to come out of Japan, Code Geass is also one of the best. I haven't seen R2 (second series) yet, but R1 is absolutely phenomenal. It's not perfect; there are a few times where characters' actions make no sense and had me scratching my head. However, I didn't care about that much because the animation is clean, bright, and nice to look at, the music is great, the action is pulse-pounding, and above all, the story is quite possibly the greatest war story ever told in an anime. I'd explain more about it, but that would just spoil how brilliant this tale is. It's basically a story of war, rebellion, morality, strategy, and the supernatural, all rolled into one. Oh yeah, and there are giant robots.
Now, as great as it is, don't go around showing this to your Pokemon or DBZ loving kid brother. For starters, Code Geass is quite violent, even as far as mainstream anime goes. Most of the action takes place in giant robots, but the action that doesn't is quite bloody. There is also some of what is known as "fan service" by the anime community (sexy scenes of female characters meant to gain a... reaction out of male fans), most of which centers on a certain female character, Kallen. It's a running gag for her to be caught in the middle of bathing by other characters. In one particular scene (in the version not censored for Adult Swim), you see both her bare butt and breasts (including nipples). Concerning profanity, d**n, h***, a**, and b***h are all used sporadically with a s**t or two thrown in if I recall correctly.
Then there's the issue of the negative messages and role models. Despite both actually being likable, neither of the two main characters, anti-hero Lelouch and anti-villain Suzaku, are particularly good people. Suzaku is a spineless idealist who betrays his own people time and time again. He's also against murder despite being a soldier. Main protagonist Lelouch genuinely cares about certain people and doesn't want to see them hurt, but his methods are questionable at best and completely heinous at worst. A lot of the show's drama revolves around how these two leads become bigger and bigger hypocrites until the very end, when their anger and passion for their respective ideals is only matched by their absolute hypocrisy. Neither of these characters should be looked up to. Other characters are much better role models, with the heavily-implied-as-Suzaku's-lover Princess Euphemia being a bastion of purity, kindness, and goodwill. There are a few messages that could be considered reprehensible, such as how some characters believe that killing is fine as long as it's in the name of freedom, but the overall message that racism is wrong is definitely a very good one.
However, if you're mature enough to handle the content, I absolutely recommend this incredibly slick and intelligent series. It's exhilerating. It makes you think. And above all else, it's entertaining.