The voice acting is of an excellent and consistent quality, and I think that pretty much all the characters have voice actors which suit their personalities. The majority of the openings/endings are a pleasure to watch due to fantastic animated sequences and theme songs. The background music which play during the episodes usually fit very well with the situation, although some tracks seem to be overused a little at first. This becomes less of a problem as the series progresses, with plenty of new music being introduced to support the story as it reaches the finale.
Moving on to the characters (best thing about this series), the original FMA focussed mainly on Ed and Al and on their struggles to regain their bodies, whereas Brotherhood also explores other characters to great detail at the same time. The majority of the spotlight is still on the two brothers, but it highlights their interactions with new characters which were not present in the original anime. New characters include a group of people from Xing (a neighbouring country), another person from the Armstrong family (who I think has become one of the coolest members of the supporting cast), and a new main antagonist. For me, the Xingese characters in particular (Ling Yao and Mei Chang among others) provide a new dimension to the FMA world, by showing us a different culture to the militaristic one we're familiar with. I think the new antagonist is an improvement on the original FMA, as this person has a much stronger and clever link to the Elric brothers' father. Returning characters from the original FMA, such as Mustang and Scar, are much more awesome and developed due to the fact that Brotherhood is 100% faithful to the manga. Plus, Winry Rockbell now has a much more active role in the story. I can say for sure that this anime has one of the best main/supporting casts I've ever seen, and you'd probably find it difficult to label any of the recurring characters (whether they are good or evil) as being either boring or unnecessary in terms of the storyline.
One of the many good things about this series is that there has been absolutely no filler at all (yes, I'm thinking of Naruto, Inuyasha, etc), which prevents the story from losing momentum. All the episodes are concise and every scene is important as part of the huge plot. The dialogue fully explains everything and is straight to the point. As multiple characters are explored there are lots of side stories, but these are all perfectly intertwined with the main story of the Elric brothers and more often than not directly influence their journey too. Like most anime series, there are things from the manga which have been left out, but these are usually just restricted to comedy moments. There has been one episode which shows a lot of flashbacks of events so far, but that's forgiven as it shows the most epic moments of the series, and also provided us with some history on the father of the Elric brothers.
FMA Brotherhood will be sorely missed now that it's finished. It is excellent in every aspect and has very little, if anything, that can be called a flaw (maybe rushed character development at first due to the fast pacing, but this quickly subsides). Each episode feels like it's too short, a testimony to how much it draws you in to the story and characters. There are moments which leave you smiling, laughing, sad and simply amazed. Try this anime, it's recommended for absolutely everyone, to newcomers and to those familiar with Fullmetal Alchemist.
