1. Character Development - Code Geass had many characters, you just have to watch to know how many, each character was pursued and developed. Some were minor, others were detailed. Lelouch's character himself, a journey really, I shouldnt have to explain.
Death Note had some characters, all static throughout. No character was developed. Yeah sure Light was a normal student in the start, but after he got Death Note he changed, sure ! But that's about it, and this occurred in probably the second episode, rest of 35 episodes you see the same character.
2. Story - Death Note turned out to be pointless in the end. I like anything, Movie, Anime or Games to have the story drive it. The story should move, develop and then conclude. The story behind Death Note was how a student gets hold of a book that kills, and he decides to make the world a better place by using it. That's all ?
This story was left behind, and the viewer would even forget this while watching the anime because the whole series was then directed at KIRA vs. L and then in the end KIRA vs. Near and Melo.
While consider Code Geass, not only did this marvellous anime have a brilliant story about the whole Colonization, Brittania, Peace, War, Equality, Racism, Power, Rebellion etc. It also pursued a deep side plot which was Geass itself. Both these stories developed throughtout and derived the whole series and both concluded in the end. Better than Perfect !