Suggestions

Moriarty the Patriot
Gurren Lagann

These two manga for starters.
anilist.co/manga/72381
O2

You have not seen many anime movies yet. I think that my top 10 might be a good starting point to experience the variety of the medium:

• Action:
  Akira
• Adventure:
  Metropolis
• Mind Game:
  Mind Game
• Drama for cildren&adults:
  Night on the Galactic Railroad
• Drama for adults:
  Belladonna of Sadness
• Fantasy:
  Spirited Away
• Minfuck:
  Angels Egg
• Romance:
  5 Centimeters per Second
• Sci-Fi:
  Royal Space Force The Wings of Honneamise
• Thriller:
  Perfect Blue

I hope you enjoy exploring the medium. <3

Ps: Not sure whether you meant a good anime like Code Geass or an anime with similarities to Code Geass. I hope that this list is still helpful if you meant the second one.

Moriarty the Patriot
^Basically it's almost like this show sits in the middle between Code Geass and Death Note, with its focus on systemic oppression being really close to the former.

Legend of the Galactic Heroes
^The best place to go if you want a show that focuses on politics, military strategy, and battle tactics, all of those being core elements of Code Geass. Also, one of the protagonists feels (in a few aspects at least) like the precursor to the type of character Lelouch would be.

Mobile Suit Gundam 00
^Produced by the same studio and at a similar time, you'll find quite a few shared themes, but with different execution. Of my recommendations, this is the only one that's also mecha.

To you I'd recommend the continuation.
Code Geass Lelouch of the Rebellion R2

Also:
Naruto Naruto Shippuden ONE PIECE Bleach Fullmetal Alchemist Fullmetal Alchemist Brotherhood Soul Eater Gurren Lagann Cowboy Bebop Trigun Samurai Champloo Dororo