***Note: this review assumes that you've read the book.***
One-sentence summary: If you squint past the time travel errors, and manage to swallow the Anakin-Skywalker-esque explanation for how the Bad Guy came to be, this is basically one giant, entertaining YA chase scene, with a nice theme of learning to love yourself thrown in for good measure.
The plot. All Our Yesterdays is YA dystopia sci-fi, without (unfortunately) actually showing the reader the dystopia. We see a hardened prisoner named Em escaping from the evil Doctor with her devoted next-door cell mate, Finn, to make their way to a time-travel machine called Cassandra, in order to travel back in time four years and prevent the creation of said machine. Based on a note written in Em's handwriting and stuffed in a drain in Em's cell, they know that this is the fourteenth attempt, and the only course of action they haven't tried is to kill the younger version of the Doctor before he can create Cassandra. Unfortunately, the younger version of the Doctor is James, Em's lifelong crush and best friend. Marina, Em's younger version, is just a girl who wants a happily ever after with the brilliant, handsome, slightly volatile boy next door, who happens to be destined to become an evil genius. In alternating chapters narrated by Em and Marina, we see the two time streams intertwine and collide.
What I liked. I quite liked Em's motivation to protect Marina, her younger self. I liked the implication that she had grown to love herself over the years, enough to have a big-sister or even maternal desire to secure her own youthful innocence, no matter the cost to her current, scarred self (Em will never have existed if she and Finn are successful in their quest). I like that we're following the exact four-years-ago timeline that matches this final attempt to destroy Cassandra, so that we get to see the final outcome for young Marina. I liked the open ending promising that her affection for Finn is growing as they mourn together. More generally, I liked Finn's and Marina's relationship, and Em's and Finn's. I also really liked the exploration of the question of whether a person is responsible for a future crime if he hasn't already thought of it--the idea of intention and free will are cleverly poked at. (I disagree with the moaning on goodreads of readers who hated that Em couldn't pull the trigger on young James. This was a wonderful dilemma she struggled with.)
What didn't work so well. There were some time-traveling glitches that made me stumble. For instance, how does Em know what happened in previous attempts (where she and Finn presumably died)? She has dialogue-specific memories from West Virginia (e.g. Rena snoring), which couldn't have been written on that tiny paper in the drain pipe. Was I not reading carefully, and that information was gleaned from one of her time-travel, epileptic-like seizures? Similarly, how could Finn have a scar on his hand (the one he fondles when he's nervous) from one of the previous attempts? Wouldn't his body reboot each time the time line fails? And why are the Doctor and the Director demanding to know where the documents are--the scribbled notes that were the "aha" inspiration for Cassandra--if Cassandra has already been successfully invented? (Also, the torture scenes were a tad cliche. I couldn't stop thinking, "Ver ahr ze papers?!" It was much more affecting to know that sometimes the Doctor came in and wanted to talk to her as his old friend; that's subtle torture.)