Well, first, you should know that this story is a good case of Cerebus Syndrome: as it progresses, it becomes slowly darker.

This is actually a good thing. Basically, the story's tone is that of Fullmetal Alchemist, not the other universe. There are very, VERY depressing moments. Selim Bradley is a lot more anti-heroic than Ed, some backstories like Kirche's are reinterpreted for the worse, and one villain in particular went from bad and creepy to a really frightening Complete Monster. You're warned.

But on the other hand, the Character Development for the different characters is handed very well, some ideas are very interesting, and there is still humor.

So, if you like dark but good stories, this one will captivate you.