Girl Genius is the story of Agatha Heterodyne, a budding Mad Scientist in an alternate history run amok, a world where Mad Science is a sadly routine part of life, and where the history books took a left turn at Albuquerque as a result. She doesn't know her true name, nor that she is one of the gifted "sparks"; however, I'm comfortable saying that these are not spoilers, since the book has been pretty clear about these points from the first preview issue. This story isn't about the mystery, nor even necessarily about where we're going; it's all about the ride.
This story is sheer lunacy: it is Phil and Kaja Foglio having way too much fun, and they can be very infectious when they want to be. The cast is full of deliciously strange characters, both the mad scientists and the results of their efforts: golems, monsters, large steam-driven mechanisms and the most arrogant cat in the entire world. Each has his or her own distinct voice and the whole story has many shades of grey painted over the top of an ostensibly black and white world. (The dictatorial Baron is not nearly as evil as he appears at first, and the self-proclaimed hero is more than a bit deranged.) It's not always deep, but it is always remarkably creative fun.
I said that this was starting at the top, and I meant that literally. I normally read my comics more or less chronologically, and I stack each week with the best stuff on the bottom, so that I can save the best for last. Thus, my usual high praise is to say that a book is at the bottom of the pile: it's one that I'm holding onto, and plan to read slowly when I have the chance to savor it. But the absolute best books are actually the top of the stack. I'm usually a few weeks behind on my reading, so the books at the very top are the ones that pop to the top of the stack because I can't stand to wait. Currently, Girl Genius is the only book on the top of the stack.
TRoOB Rating: A
(I mean, really: how cool is a book that has its own secret code, and includes coded messages in every issue? I even got inspired, in an ultimately geekly moment, to write a fancy interactive decoder applet, for those of us who don't have the patience to fiddle with the secret decoder ring that came in the preview issue...)