I think I'm glad I saw the anime first (haven't yet tracked down "Brotherhood" because when I tried to get to the advertised free-and-legal streams I crashed my computer), because I loved it and yet the manga is so much more complex. Encountering them in reverse might well have disappointed me.

I've bought up through 18 or so, read through 15 or so, and forgotten huge chunks. That's the problem with series, for me; with each new release, I have to go back and reread all the previous to remember what the heck is going on. I find that with most anything, but especially with FMA, because there's just so much going on.