Recently, my husband Andrew and I began watching Fullmetal Alchemist Brotherhood. Though there are some similarities with the original Fullmetal Alchemist anime, Brotherhood follows the original manga plot and is very different than the first Fullmetal. The new anime is much darker than the original one, even though the original was pretty dark to begin with. In my opinion, Brotherhood is significantly better and explores the world of alchemy more in-depthly than the other anime. You learn more about the history of alchemy, and the Brotherhood's story line is vastly different than the original. The original Fullmetal and Brotherhood plots are similar in the beginning, but with the death of an important character the two plot split and create two very different stories.
Many of the characters have very different fates in Brotherhood, as well as a whole new cast of character not even in the original. The first Fullmetal gets no where near as in depth into the world as a whole, and it is nice to learn more about the Fullmetal Alchemist world. Though both animes are some of the best I have ever watched, I have to say Brotherhood is my favorite and I love the true to manga storyline much more.
I do understand why they changed so much of the plot, though. Brotherhood, as I said in the beginning, is much darker than the original Fullmetal Alchemist, and not something I think would be appropriate for younger viewers. The original is not something I would let younger children view, but Brotherhood takes it even further and can be, on occasion, a difficult to watch. I recommend viewing both before letting young children watch as there are some disturbing concepts illustrated in Brotherhood, but for any anime fan or fans of dark, thought provoking shows this is a must.