Overman King Gainer, Bounen no Xamdou Recommendations
Wacky, Wild, Biopunk, futuristic, and mecha. Definitely similar.
Both series have similar aesthetics courtesy of character designs by Kenichi Yoshida. And either series is mecha with elements of biopunk - particularly in Xam'd, which isn't tagged as mecha.
The key difference lies in the tone/mood. Overman King Gainer is upbeat and fast-paced, while Xam'd: Lost Memories takes a more somber approach. In either case, the setting and details take a while to be fully fleshed out.