More Happy Than Not

Good, but not great.
At the beginning of the book too many side-characters are introduced, and except for two of them, they are so blandly described that you struggle to remember who is who for the rest of the book. Unless you make the characters really outstanding, not even seasoned writers with decades of books' worth can make it work - even Stephen King has been guilty of this in later years.
I didn't feel as much for the characters as I did with “They Both Die at the End” or “History is All You Left Me”. Of course, this is Silvera's first book, so some rough edges are to be expected.
And now to the twist ...
SPOILER
When we a little more than halfway through the book learn that Aaron actually had the procedure at Leteo, I felt cheated. To me it was a cheap twist that just seemed like an afterthought. It made it all more confusing and made me doubt how much of the rest of the book was real or false memories or whatever. Overall the whole Leteo thing actually didn't sit well with me.
All in all, worth a read, but don't expect anything groundbreaking.