Before I Go To Sleep is okay. The writing is nicely tense, and Watson does a good job of creating a sense of foreboding as the reader discovers what's going on at the same pace as the narrator. The book feels a little gimmicky, but the writing isn't bad.
The main character in this book has the kind of amnesia where your short-term memories disappear every time you go to sleep, and never make it to long-term storage. Or at least, aren't accessible there. She's 20 years older than she remembers, and wakes up every morning next to a man named Ben who says he's her husband.
And every day, her doctor calls and tells her where her journal is, so she can see what work she's been doing to recover her memories. But she keeps the journal hidden, and the front page has scrawled on it "Don't Trust Ben."
So it's unsettling to read, but not the sort of unsettling that crawls into your brain and nests there. I finished this a couple of days ago, and can't honestly say I've given it a thought since then. It's pop fiction, and there's nothing deeper.
And that brings me to the ending, which quite frankly broke my willing suspension of disbelief, in that we're told things about one character's psychology that make all of that character's previous actions unlikely, to say the least. At the end of the book, we're told that the man who has been masquerading as Ben can't deal with the unexpected, or with complications. However, the entire previous part of the book has been about him improvising, keeping ahead of the main character as she poses unexpected challenges to the life he has created for them. These two things can't be simultaneously true.
While I was willing to buy into this fairly slight thriller until that point, this incongruity completely broke any sense of suspense. So this is a fairly well-crafted thriller, with a huge hole in the last 30 pages.