This is my very first review so I hope it's gonna be helpful and there won't be too many grammatical errors (English is not my native language^^).
Before watching Code Geass, I had been told a LOT of good things about it. Though I really enjoyed watching it, and it is a great anime, it didn't totally live up to my expectations.
First of all, the story :
It is pretty good overall, there are some very good twists. But I have 2 problems with the story : First, at some points in the story, everything is happening way too fast, and I got kind of lost. Also, there are lots of things I wish they explained, or stuff happening that didn't really make sense to me (just a few things... but I don't want to spoil^^). But I guess I'll get some of the explanations in season 2. So yes.. too much stuff happening but if you can follow the plot it's a great story. The good thing is, it often goes so fast that you don't have time to think about it XD
There are also some pretty funny moments. I really enjoyed the cat (Arthur)^^
And one more thing : I don't like big robot fights AT ALL... but it didn't bother me in this anime. I think the plot is more important than the fighting anyway in this one^^
Best part of the season i.m.o. = episode 22, at about 15 minutes :P So unfair but I think it was the best twist in the whole season.
Not much to say about it, and I'm not an expert so ... let's just say it's was very good i.m.o.
I didn't like the endings and openings XD But that part I can skip so I didn't care hihi And anyway it's just a matter of personnal taste I think.
Not much to say about the sound either except that lol I don't think I'm able to really judge it^^
I really enjoyed a lot of characters (Suzaku, C.C., Euphemia, Cornelia,...). There are 2, though, that we could say I had trouble with. First : Nina. I HATE this character, I really really hate her. She does nothing and it's like she's here just to be a creepy little character. I like creepy characters, but she is just annoying. And Lelouch... Let's make it clear right now : Lelouch is a great character and I didn't hate him... not all the time XD It was 50/50 actually. There were just so many times when he reminded me of Light (Death Note), and I hated Light sooo much XD They have a lot in common : both are students who are given a special power and they want to use it for "justice" .. and then... they start overdoing it .... and they want to rule the world. In fact I guess we could say I really liked Lelouch but I hated Zero^^
Another thing that I really enjoyed about characters : there are strong female characters! (Yeah! Girls power XD). If I only had to give one example I'd say Cornelia. She's awesome :P
So, overall I think that's an anime you have to see. It might be more enjoyable for boys than for girls (it's just my observation, I can be wrong^^) but as a girl I really liked it. There are some weaknesses in Code Geass but even though I don't believe it is the best anime in the world (as my friends have been claiming since they watched it^^), it is still totally worth watching.