Kemono no Souja Erin's first twenty or so episodes are offensively slow-paced. This, combined with the fact that it's a children's show, will probably turn a lot of people off, which is a shame.
Even though the first two arcs of Erin were slow, they weren't needlessly so. The pacing eases the audience into Erin's world, while introducing the characters and customs at a pace the target demographic could keep up with. As a fantasy series, a lot of background information is required to "get" the world, and Erin does a wonderful job at that (the only thing I wish had been explored more thoroughly were the Mist People). Additionally, oodles of information introduced in this build-up will be important to the story later on, even though it seems pretty minor at the time.
Once Erin finally gets going, it is quite an experience, though. Her experiences with Lilan were especially moving, and showed just how great of a story this is. The middle twenty-ish episodes, if judged on their own, would easily get a 10/10 from me. I wouldn't change a thing about them, I teared up at least five or six times.
The quality decayed slightly, yet again, in the last handful of episodes, as the focus shifted from Erin to the politics of the world. I personally couldn't care less about the various nobility and their issues, and felt the civil unrest was being milked for cheap drama instead of focusing on the clear-cut best part of the series- Erin and her beast raising.
For the most part, Erin's animation was thoroughly average. Flashes of brilliance (such as the stylishly abstract scenes whenever a beast attacked, or the hauntingly beautiful dream sequences and second OP) were hampered by character designs that were too plain to adequately express a full range of emotions and rampant cost-cutting in the form of an over-reliance of flashbacks and reused footage (which happened at least once per episode, without fail).
Super. There were a few really excellent songs that were played again and again at emotional moments, and after a short time the songs themselves start tugging at your heartstrings because you associate them with all these beautiful scenes.
Erin is amazing. And why wouldn't she be? There were fifty episodes almost completely devoted to developing her character, and she evolved so much during that time, it'd be impossible not to like her. She shows enormous feats of courage, strength, insight and maturity.
The other characters are much more of a mixed bag. In what I assume to be an attempt at humor (Erin's humor is terrible, by the way, thank goodness it rarely attempts to be funny), the egg thieves Mokku and Nukku were added who never failed to grate on my nerves. Them and John (who I also found annoying, though your results may vary) made the second arc rather less enjoyable than it should have been. Most of the other characters are interesting but don't get anywhere near enough screen-time to become attached to. The main villain in particular was really shallow.