The superior version of Code Geass is Legend of the Galactic Heroes. Code Geass seems to have taken a fair bit of inspiration from it, that being almost the entire premise and a fair bit of the plot. Legend of the Galactic Heroes is a space opera on a scale bigger than Star Wars.
Instead of Guilty Crown I would recommend Neon Genesis Evangelion. Guilty Crown is a weird amalgamation of both Code Geass and Evangelion. Evangelion is a good character study, though is lacking in other areas.
Many people seem to think Log Horizon is SAO but better. I've not seen Log Horizon, but there may be some truth to it.
If you want a violent and gory show, Hellsing Ultimate and Devilman: Crybaby are quite good. Elfen Lied is just dated.