So, yes, very educational -- lots of history, lots of science, lots of literary references, lots of moments of having to use good judgment, lots of sibling behavior lessons, etc.
I'd downloaded #1-#6 from iTunes onto my iPod a while back for our last vacation and they've listened to them religiously ever since. Mommy, though, finds the audiobook voice of Annie very creepy (I know, sounds like a potentially juicy therapy session to me, too), but we may have to take a step back from technology on this one and go with the real live paper and ink versions to maintain familial harmony.
So then as luck would have it, while visiting Tia Sonia last week, I came upon books 7 and 8 and quickly snatched them up. The kids happily devoured them within minutes and are now ready to move on. Logging onto the website, I was excited to discover that there are at least 37 more that we have to catch up on. They're pretty easy reading for the kids, and, apparently, there's even a musical (although sadly mostly touring the midwest). :(
So here are links to the first 8 in the series that we can personally recommend: