For perhaps the first time ever after reading a Mitchell book, I wished he hadn't set it in the same fantastical world as a previous novel (i.e., The Bone Clocks). Mitchell is such a good writer, and I don't really want to read a series by him, I want to read unique and diverse offerings.
It's not that I wasn't intrigued by where he was going here. You feel the angst and the horror and the thrill and, above all, the oddness of this story. Plus he gets to give a fabulous speech on the deficiencies of humans who can't remember their own history, which, if it wasn't hugely depressing would have had me smiling. But the story became, well, repetitive, and when the final solution reveals itself, it's rather deflating.
I'll give him a bit of a break in that this book feels more like a novella than a true novel. It's possible he wrote it as a short story and then developed it into a short novel? I don't fault him that, but I do hope he writes something wholly different next time around.