Agatha H. and the Voice of the Castle: A Girl Genius Novel - Phil  Foglio, Kaja  Foglio
When I started this, I had one big question: since I hadn't read the comics this one was based on (unlike the first two), would that effect my understanding or enjoyment of the novel?  Nope.  Not a bit.  Which I think is a good thing.
Like the other two installments, this is just fun to read.  The writing is full of joy, zip, and panache.  The narration, descriptions, characters, and escapades are just fun.  I couldn't tell you how often I had to stop to chuckle (or more) at what looks like a throwaway line, but probably took 5-6 tries to get just right -- and was absolutely worth the effort.
The whole gang is back -- plus a few new characters, most of which I want to spend more time with (others I've already had my fill with).  I think the city and residents of Mechanicsburg are great, and I hope we get to spend more time with both.  Ditto for a certain self-aware piece of architecture.  I still love the Jaegers, even if I typically have to stop and really think about the pronunciation of every one of their syllables -- which, honestly, makes it more fun.
My only complaint -- well, I have two, actually.  The biggest is that the last 100 or so pages seem like the authors are just spinning their wheels.  Which is just frustrating.  The other is a common one for me -- anytime another person takes over someone's body, so that it's hard to tell who's doing what?  Boring.  Hate it.  Silly plot contrivance that I hope goes away soon, but will probably stick around for a long, long time.  
Still, not enough to crush my enjoyment of the book as a whole and or to keep me from wanting the next one soon.
If you've read the first two novels, there's nothing for me to say other than, keep going.  If you haven't -- don't start with this, it won't make sense.  Go back to <b>Agatha H and the Airship City</b> and enjoy.