A simplistic blurb describes the series as about two brothers who, after having failed to resurrect their mother through alchemy and paid a heavy price, go in search of a way to restore their original bodies. When I say this it not even the half of it, I am not exaggerating in the least, but since I knew almost nothing of the series going in, I don't want to delve too much into plot details, as I took great joy in watching the story expand and grow.
Perhaps the best way to recommend this series is to compare it to Avatar: The Last Airbender. Alchemy resembles bending, as alchemists manipulate rock and steel and fire in combat. Like Avatar, FMA tackles genocide, but it also examines the lasting effects on both the survivors and the perpetrators. The show has badass female characters aplenty—"badass" does not always mean "good at fighting"—and although some of them have romantic plotlines, the romance never diminishes them as women; in fact, they are usually protecting their male love interests. Honestly, I boggled at the introduction of each new amazing female character because each one was so different and interesting, and they were all in this one show, when some shows can't even manage to get one interesting female character. And, just like fan-favorite Toph isn't introduced until a third of the way into the series, some of the best characters in the show aren't introduced until later, and it never feels like new characters are simply being added to fill time: each character has a purpose. In fact, each character has his or her own agenda. Even the "good guys" comprise characters who are not necessarily in it for the same goal, and the "bad guys" don't all march to the same drum either. Hell, some characters switch sides. The amount of character depth in this show is astonishing, given how many characters there are; it would be so easy to make them all one-dimensional, but no one is a cardboard cut-out. It also has a good sense of humor, with many amusing running gags and exaggerated, clever reaction sequences.
Season two of A:TLA is one of the best seasons of television I've ever seen. Amazing characters, interesting villains, moral greyness, and, most importantly, incredible narrative momentum as it hurtles toward the finale with plot twist after plot twist.
Fullmetal Alchemist: Brotherhood is 64 episodes of that. It would regularly cause my brain to melt into a puddle of capslock. But in addition to being a rip-roaring story, it's packed to the brim with thematic content and emotional resonance. Fathers and sons, brothers, love, friendship, guilt, regret, greed, redemption, the role of the military, national pride, national shame, revenge, forgiveness, power, humanity, immortality, life, death, and so on.
Even though I spent this entire review comparing the show to A:TLA, the truth is that I have never seen a show quite like Fullmetal Alchemist: Brotherhood. It's fucking amazing, and I already miss all the characters.