B't X stands out as a very unusual and unconventional series, in my opinion, and an exciting ride. Made by the famous Masami Kurumada, the guy who ended up inspiring Sailor Moon, the entire shoujo group CLAMP, and numerous shonen stories after it, it was made in the mid 1990s, after the forced conclusion of the famous Saint Seiya. Similarities can be seen, however, in B't X, none of them detracting from the experience.
In the futuristic Earth of B't X, humanity has made amazing progress in artificial intelligence, and the pinnacle of these robots are B't machines, pronounced like "Beat", as in a heartbeat. A B't cannot work unless its core comes into contact with a person's blood, wherein they take on some of their characteristics. However, the B't is its own entity, capable of independent thought and also not bound by the Three Laws of Robotics.
Our hero is Teppei, a young Japanese man who bears a resemblance to Kurumada's previous hero Seiya, and shares his predecessors' hot-blooded nature. His brother, Kotaro, was studying robotics in Germany for five years before the start of the series, only to return to the Orient for an exposition. Unfortunately, Kotaro is kidnapped by the Machine Empire -an organization located in the Gobi Desert- for reasons unknown to Teppei. Nevertheless, Teppei pursues the captor, armed with the light-producing Messiah Fist, but upon reaching the Empire's base of operations, is beaten within an inch of his life. Thrown into a trash heap filled with broken B't units, Teppei's blood comes into contact with the discarded Kirin-type B't known as X. X awakens, and reluctantly saves Teppei.
Things get interesting from then on, when the readers discover the Empire's somewhat-justified reason for capturing Kotaro, and a cast of colorful individuals. Teppei finds support in a quartet of rogue members of the Empire, the Four Knights, and their B't units, and the enemies they fight on their way through the Empire's fortress have surprisingly deep backgrounds for having short screentime. Battles have a certain level of scientific know-how to them, but things are kept simple enough that you don't need to take a physics class to understand what's going on.
The series had an initial run of 25 episodes, but the series was wrapped up with a 14 part OVA miniseries that aired one year after that. Tokyopop also publishes the manga in America, and I've read a few volumes and really liked it. There's a lot of tragic moments in the story, and points that really flesh out the various characters. Fights never resort to formulaic DBZ-style one-sided beatdowns, but some fights do seem quite hopeless for the protagonists. Probably the biggest example was when Fou Lafine, an atheist monk (don't ask), was up against an opponent who essentially was omnipotent and at the same time
didn't exist. He still won, in a way that didn't seem stupid, but it was really an emotional end for a battle that pushed him to his absolute limits.
Anyways, give it a look if you have the chance. There's no other story out there like it.