Sunrise and Tohokushinsha (two companies that created the original Raideen) got together to make a modern version of Brave Raideen. The two stories are completely unrelated, and homage to the original Raideen's design is paid only in the design of God Reideen in this series.
Ten members of the ancient warrior race of Reideen awakens in the body of ten teenagers to battle the super demons. The super demons who lost the battle to the Reideens in the ancient past is bent on winning this time by awakening the God Reideen to use against the Reideens.
Each of the ten Reideen character takes a form from a bird which gives them their unique style. Each can transform themselves into god bird in the heat of the battle as Brave Raideen did. Every episode features different super demon and story builds to the awakening of God Reideen. Twist to the story is that God Reideen is an engine of destruction, and goes to destroy the world.
Chouja Reideen was originally scheduled to finish after 26 episodes but due to its popularity, was extended to 38 episodes. Maybe for this reason, the first 27 episodes and the last 11 episodes have different feel to the story. First half deals with super demon's attempt to collect 12 orbs of the zodiac to awaken God Reideen. Second half deals with strange battle that ensues between the Reideens.
Characters were designed to capture female audiences (there are many women anime fans in Japan), and heroes turning naked during transformation and after was put in to appeal to this target audience.
The quality of artwork gets better as the series progresses, and the last 10 episodes are truly stunning.
Watch the first half of the series for the story, and watch the second half for its surprise ending.