FMA Brotherhood is an adaptation of the manga plotline. There are some additions (ep 1 for e.g.). The overall plotline, I think is better here but the anime just seems to rush through most of it.
The original is a separate story, anime exclusive although the beginning in both are pretty much the same. Different villain, different methodology, different analysis of the story etc.
I'm very fond of the original anime but the Brotherhood so far has been excellent.
Also, the music in the new one can't touch the original.
@ Blaso, thanks.
but I hate watching online, downloaded from AnimeTake.