This book felt like a perfect end to the series. I loved the first book, but felt like the second book was a bit slow, too lengthy, and filled with mini info-dumps. "Lark Ascending" is the perfect combination of books one and two; it had rapidly-developing characters and fast-paced plot like the first book, but continued to build upon the world and provide more information about the society in which Lark lives like the second book. The result of this combination is an absolutely amazing science-fiction/steampunk/fantasy read that will have you on the seat of your chair from the first page to the last.
I will admit, the beginning of this book was a little rough for me, not due to the writing but simply due to the fact that Spooner wastes absolutely no time recapping. You are expected to remember where we left Lark in the second book all on your own. This is one of those series with so much information that it would be best read the books back-to-back. It did not take long for me to remember what was going on, though, so no harm done.
One of my issues with book two was that it tended to have large lulls in the plot, making an already very long book feel thousands of pages long. This third book did not have that issue at all. From the very first chapter there was always something happening to someone, whether it be Lark, Basil, Eve, Kris, or Oren. In addition to pace improvements, the story is also jam-packed with even more information about Lark's world and its origins. Spooner had already done an absolutely magnificent job creating a believable world by providing readers with tons of detail--this book just takes that to a whole new level.
The characters are also fleshed out more in this final volume in the series. Backstories, origins, and relationships between characters are all fleshed out really, really well. My favorite details were those of Eve. I would love to see a prequel or a novella revolving just around her, but the bits we are treated to throughout "Lark Ascending" should not be discounted. I appreciated her story the most because it has so many facets--when watching Eve's life through flashbacks about the past and from Lark's perspective in the present the reader is able to feel sad, happy, scared, unsettled, horrified, relieved--the emotions run the whole gambit. We are also able to see Eve come full circle. She was just a normal girl, who ended up trapped in a laboratory that drove her literally insane. This, to me, makes her the most complex and interesting character in the entire novel.
Aside from my complete adoration of Eve, I really enjoyed what Spooner did with Lark and Oren's romance. It is never over the top or cheesy, just honest, sweet, and comfortable. Also appreciated the fact that Spooner has a really fantastically set up potential love triangle but chooses not to use it in favor of friendship. Normally don't see that kind of thing in YA Fiction, so it was really refreshing to see something different.
Overall, I really loved this book. It was fast-paced, filled with well-developed characters and wonderful world-building. If you like science fiction/steampunk/fantasy books which are light on romance and love triangles but heavy on world-building, you will love this series and you should go out and pick up the first book, "Skylark", right now.