It's based on the first anime. In that one Ed went to the other side of the Door, which is our world, while Colonel stayed in their own world and retired to a iced place. The second par is after the film, in which the Colonel returns to service, but their still in differernt worlds u.u
Oh damnit :OO I only saw brotherhood :OO am i missing out so hard ??? please tell me, I'll watch the whole the right away!!
Missing out... Well, I watched the first anime first, and I actually enjoyed it a lot it's own way. However, you must be prepared for drama and quite a bitterseet ending, in contrast to Brotherhood (which is the one following the manga's original story, and that way being the "most canon").
To me, it's worth watching, it's like an alternative universe with different explanations for the events, and even the origin they give to homunculi is completely different as well (some homunculi are other characters instead of the original ones, Sloth is completely made up).
Which anime is better? In my opinion, Brotherhood. The first one is interesting though, it goes through the first part in a slower way, and there is music you NEED to hear, specially "Bratja", that one is beautiful. If you don't watch the old anime, at least listen to it's music, the openings and endings are awesome, and so is the soundtrack.
And like (almost) always, manga better than anything else.
Hope I was of help :)
Why exactly are they separated???? Q.Q