Funnily enough, I just read Firestar's Quest
last night (I got it from the library). I didn't know there were two new books out. I might read the new manga in the bookstore, since I can never find it in libraries and I'm certainly not buying a book that takes, what, 15 minutes to read?
They're entertaining books but not great art. It's hard to keep characters straight since every cat in the clan seems to have one of the same three names.
No matter what the authors (there are two authors working on the series, neither of whom is actually named Erin Hunter) say about basing the cats' behavior on studying ferals, the cats behave like people in little fur suits, not like cats. (I especially love how each feral queen appears to have only one litter, so that they don't have more children than would be normal for a human woman.) But that's pretty much par for the course in animal stories.
I have to admit the thing that bugs me most is the bit in the very first book about how neutering cats is bad because it makes them fat and lazy. That's just what we need kids to be reading, right?
That said, like I said, they're entertaining (obviously I liked them enough that I read them all from the library, although I haven't bought any of them.)
If you like fantasy cat stories, Tailchaser's Song
by Tad Williams is many times better (although of course the cats still act like people, but like I said, it's the rare animal story where that's not true).