I'm not a fan of the first series because it deviates from the manga storyline A LOT. Whhhaaat. You have to read it! It's my favourite manga of all time - and that's saying something because I read a lot of manga
The FMA is just too amazing. The reason FMA Brotherhood was produced was because the author wasn't happy with what they did in the first series. I read them from my local library in Australia..it stock the whole series! I haven't finished watching FMA brotherhood yet but I know there are some differences. You won't regret reading it - promise! But if you recently saw FMA brotherhood you might want to wait a while before reading the manga as you might get bored from repeated story elements..