Missive is a choice-based optionally-puzzly CYOA. I played through it several times, including to a final “correct” outcome.
Missive tells the story of a troubled (some might be inclined to say alcoholic) protagonist who receives a box full of old letters from an ex-girlfriend. The letters hint at an unsolved historic killing. Depending on player choices, he may discover something about the truth of the letters, or develop his relationship with his ex-girlfriend in the present. (He may also drink a lot more than I let him. I don’t know what happens if you pursue that angle on the story.)
The puzzles mostly involve solving clues left by one of the original letter writers in order to pick which of several possible follow-up letters to read. I did not get these. There were a couple of letters in which I was able to pick up some pattern of words or concepts that suggested an answer, but more often than not, even having activated a mode that is supposed to show the important words for easy identification — even after I’d managed to guess right and gotten the guess confirmed by the endgame — I still didn’t quite understand how the puzzle was supposed to work.
The stories worked better for me than the puzzle content, though the story told by letters was sometimes stilted by the demands of the puzzle to the point that I didn’t always believe these were messages written by real people. The relationship with the ex-girlfriend has some good moments of human observation, and the bit about how the protagonist feels about her painting her nails stuck with me.
In any case, I had some fun with this, and I think I ultimately understood what happened in the mystery, mostly. (I got all the puzzles flagged as right, anyway.) I wish I understood the puzzles more fully though.