Breathstealer is my favourite Erin Hunter character, she's so good and I can't wait to find out what's the endgame with her.
Bravelands in general has been amazing (especially past arc 1, but it was good, too) and is criminally underrated.
Three book arcs mean that the story is tightly written and we avoid the Warrioresque book 4-5 slump. Greater timeskips avoid continuity snarl, while still preserving the sense of it being the same world, with occasional throwbacks to the previous books. It's familiar, yet it feels fresh, too.
Changing the species each arc means that we get to expand the setting, especially since the cultures of different animals can be drastically different.