There are a couple of good surprises, one early-ish and one pretty late. (Trying to avoid spoilers here.)
The early-ish surprise (a character reveal) was a genuine jump-scare for me and I knew exactly what was about to happen. So pretty good.
The later surprise (a revelation about why someone is in their situation) is actually subtly foreshadowed better in the movie than it was in the book. A really great improvement.