If you liked the Brain Powerd anime, the Anime-Planet community thinks you'd like:
In the future, a devastating event known as Second Impact has destroyed Tokyo as we know it, giving rise to Tokyo III - a city under siege by mysterious lifeforms known only as Angels. Mankind's only line of defense are the Evangelions, a set man-made machines piloted by a trio of fourteen year-old teenagers, Rei, Shinji, and Asuka. The fate of Japan and the entire world now lie with these three children, though they might not have the power to save the most important thing of all: each other.
Both these series deal with human pilots and their interaction with their robots, plus the complexities of human nature.
Both series contain alien fighting machines (Antibodys in Brain Powerd, Angels in Neon Genesis Evangelion) that pose a threat to the world and opposed by a small organization that uses young individuals to pilot powered suits. Both series focus not only on the fighting of mecha, but also on the emotions and psychological condition of the pilots. If you enjoyed one series, you will probably enjoy the other.
At the dawn of the twenty-first century, a sudden climate change known as the Equatorial Winter devastated humanity. The survivors saw the new age as an opportunity to create a unified world order. Driven by this vision, the United Nations officially declared a war to determine which country would become the first world government, a war they named the Wisest World War. This conflict would be carried out not between soldiers but between individual mecha known as Gigantics. In such a restless world lives Shingo Suwa; he has just beaten hundreds of candidates to the position of pilot for Japan’s mecha – the Susanoo. But there is far more to the Gigantics than meets the eye. Is Suwa truly prepared for what it takes to fend off all the other champions and bring victory to Japan?
Both Brain Powerd and Gigantic Formula use mechas that aren't quite of the traditional formula. Rather than big stompy super powered mechas piloted by brilliant individuals, the mechas in this series have minds of their own. Indeed, the mechas in these series actually choose their pilots to a degree and react to their will and feelings.
In addition to the above, there is a similar story line in which the characters are trying to forstall an event that might result in the destruction of the world, caused by the very beings they pilot.
It is my firm belief that if you watch both of these series, you will find many similarities and an equal level of entertainment.
Far, far away in a distant time, there is a tribe of people called the Golden Tribe who have the ability to create stars and foretell the future. They gave out a warning to those who have yet to mature: 'Move.'. Three tribes answered their call: the Silver Tribe, the Bronze Tribe, and the Heroic Tribe. Soon after, the Golden Tribe encountered a crashed ship in which only a baby human known as Age survived; they named the child's race the Iron Tribe and assigned one of the few living members of the Heroic Tribe to protect him and his race. Now, in a distant part of the galaxy, humanity is threatened with extinction at the hands of the other tribes. With only a prophecy to go on, they set out to the deepest depths of space to find their savior named Age -- humanity's last hope.
I'm not quite certain why exactly you would like Brain Powerd if you enjoyed Heroic Age and vice versa. Maybe it has to do with the fact that feelings and relationships are a big part of both series as opposed to lots of fighting (though there is plenty of that too) or the fact that the mecha are more organic and their pilots have a more personal relationship with them (though in Heroic Age the pilots and their mechs are almost indestinguishable). Regardless, I think both of these series are similar on several levels and if you enjoyed one, I think you will enjoy the other.