It's methodical and almost paced... but not slow. Simply more careful and thorough than a lot of anime series take the time to be. Like 12Kingdoms, this reminds me of the experience of reading a novel, although 12K was much too slow at points. Seirei no Moribito feels like an epic series in gradual advancement. My interest in the plot is high, the world of the characters is new but familiar enough not to be a big issue, and the characters are already strong and three-dimensional.
I'm most impressed by the choice of protagonist... a stoic, conservative female warrior on the brink of turning 30, repenting through past evils and seeking a higher way of life without needless killing. Not only is it unusual for anime to take what would normally be a stock "male" role and make the character female instead, but it's unusual for any anime to have a female protagonist whose older than 25. And now this woman, who has been a drifter for her whole life, is suddenly saddled with a child... a self-conscious, spoiled boy of about 10-11 years. He's not a bad kid-- in fact he seems to take it to heart how much other people have sacrificed and continue to sacrifice for him--but he's immature and unsure of himself, and has practically no useful skills.
The eclesiastical character--Shuga-- I also find him interesting, and I look forward to the future events that make his plotline overlap with Balsa's. I can't help but feel that the whole empire is going to go through some significant changes before the end of this show... we see little hints of conflict in the clergy, in the royal family, and in the spy network connecting everyone to everyone else. I just know the camera doesn't pause on the covered faces of the servants so often for nothing.