Full Metal Alchemist changed my life.
The anime made me appreciate my brother more, encouraged me to persevere to reach my goals, and enabled me to meet two of my very best friends.
The manga actually taught me a lot about writing. Even though I have no desire to write a manga, Arakawa-san is so good at weaving stories that I learned a lot just from soaking in this masterpiece of a story. I learned about pacing, cliff-hangers, foreshadowing, tension, secrets, plot twists, character development (which, in Ed's case, was visual as well as internal), and the balance of the serious and the humorous. Perhaps most importantly, I learned how to do romance right. Watching the way she handled various pairings in her manga, and writing fanfics that attempted to stay true to her characters, made me see how if you understate things and just give subtle hints, it's ten times more powerful than if you describe in gushing detail everything they do or think or feel. That's extended beyond just romance and into many aspects of my writing.
So I guess, in a nutshell, the FMA manga has taught me the value of understatement.