I recently finished reading Mainspring by Jay Lake. It is a definite steampunk novel with a very interesting premise. Nearly all steampunk is set in an alternate history setting, but this one is set in a completely alternate world: The Earth literally orbits the Sun on gears, the Moon orbits the Earth in the same way, and a giant gear at the equator (it extends 100 miles from the surface) makes the northern and southern hemispheres almost entirely isolated from one another. It's orrery-as-reality. The major conflict is introduced in the first chapter, when Gabriel appears to the protagonist to inform him the world's mainspring is running down, and tasks him with traveling halfway across the world to wind the mainspring. You find out early on that this is one of the things Jesus is believed to have done (although the evidence is apocryphal).
At its core, the book is merely an exercise in worldbuilding. Most speculative fiction has at least some element of worldbuilding, but in this particular book, the world is so compelling that I would be willing to follow just about any journey into it. In other words, the characters and plot are of secondary importance. Which is not to say they're not worthwhile. Most of the characters are flat, and there are groups of them which are mostly undifferentiated, but they are all believable, acting in consistent ways. The plot does have some moments which could be accused of being Deus ex machina (excuse the pun), but they all make sense in context (in any case, I think there was just a tiny bit less foreshadowing than I would have liked).
My biggest complaint is, as with my last book review, the love story. Here it's not because it's unbelievable, or not compelling, or that it fails to advance the story. It's just weird. I mean, really freaking weird. It turns out to be necessary to the plot, but there are at least a few ways Lake could have written around it. Some of them would have required making the book longer, but anything would have been an improvement. Even with this very weird element, the rest of the book is so compelling that I could easily get past it.
Now, I feel I have to address some of the characterizations of the book as blasphemy, as some reviewers have done. I think it's better understood as taking the speculation in the speculative fiction to its logical extreme. Here, that means asking the question, "What kind of God would make a world like this?" or "If we change the world in this way, how would God treat the world differently?" It's not all that different from C. S. Lewis's The Chronicles of Narnia, where he asked, "What might Christ become like if there really were a world like Narnia . . . ?" Which is not to say Lake was asking that question. Indeed, he does not wholeheartedly embrace any single alternate theology. As in the real world, the characters are not given plain answers to those questions.
In sum, the world is extremely compelling and absolutely unique, the characters are believable, and the plot is intriguing. In all, I give it 4 out of 5 stars.