Like others, I'm often a bit skeptical about collaborations between authors, be they both well-known authors or not. In this case, I was very worried because their styles are very different and they take an amazing jump between hard-SF and character-driven world-building fantasy. 
 HOWEVER, I couldn't be more pleased with the combo. I was thrilled by the characters and felt the wonderful sense of adventure and then suspense as things got dire. And that's just it. We get the best of both worlds, the hard-SF premise that promises to throw us into a very, very large setting because we're traveling through hundreds of thousands of alternate Earths as people "step" through them, getting the implications explored, from economics to law to nationhood and all the way back to what it means to be an individual. 
 But what's more, it's a rip-roaring fun ride, with the classic iconoclastic loner with a unique ability to travel quickly between worlds and a truly fantastic Coke machine that thinks he's a human, (Really, he's a Buddhist AI airship, but who's counting?) 
 And through all this, my expectations for a fun story, great characters, heavy science (explained easily or even just glossed over for the sake of speed, while also remaining accurate), and world building and plain imagination is all thrown into the same bag. I loved it. 
 I'm a Baxter-phile. I'm also a Pratchett-phile. I don't know WHAT the hell I was thinking about avoiding this so long! On to the next and the next, I think. I may not get to anything else as I fly through these fun novels. :)