If you loved the eerie, meta-narrative style of 'Dear Mr M', you might dive into 'House of Leaves' by Mark Z. Danielewski. It’s a labyrinth of a book, literally and figuratively, with layers of unreliable narrators and footnotes that mess with your sense of reality. The way it plays with form feels like a puzzle, much like Herman Koch’s work.
Another gem is 'The Silent Patient' by Alex Michaelides. It’s a psychological thriller with a twist that lingers, and the unreliable narration echoes Koch’s knack for keeping readers guessing. For something darker, 'The Dinner' by Koch himself has that same unsettling vibe, where ordinary settings unravel into something sinister.