An possible example would be if Zachary Sergi didn’t intend Prodigal to be a romance but found when player testing alot of people actually thought she was the fun kinda crazy. He may have planned it all along but if he didnt that would be an example. Things the players were interested in you didn’t expect and made the experience better when you added it in.
And Playtesters what feedback of yours did you not expect to be noticed but was and was accounted for?
Wow, that would be a lot. But i listened to like 80 percent of the feedback from my beta testers when it comes to Equia: Artifacts of Zazkor.
Same goes for the sequel, i even allow the readers to make some of their characters and then i just fit em in with the background and lore, and put the in the game.
I didn’t have a lot of things planned truth be told, many of the scenes were added due to readers request or just the feedback. I lost count by now… 
It’s always fun nonetheless.
Just last month, I rewrote an entire section (tripling its size) of alpha-copy based on feedback given.
The feedback I received after the rewrite made all that effort worth it.
As a tester, I expect all of my feedback to be noticed but necessarily actionable … meaning I expect the project editors/authors/developers to consider what I say, even if they then decide to ignore what I say.
The most surprising feedback action taken from my testing involves a MMO title that I tested for and an entire deployment of content was delayed because of the flaws I found. It cost the company a lot of money to do that, but they did; it was the right call.
I’m currently rewriting the majority of my game to restructure it and make it into something a bit less tedious because I got feedback that targeted overarching problems with how I wrote it and how I portrayed the characters. The game is going to be a lot shorter, but it’ll also be a lot more interesting.
For me it is the feedback relating to people wanting to add Denise and Victor as RO. While the requests for Denise were unexpected I could still see why people could like her. But with Victor I wrote him to be an unlikable person so the love he got was surprising to say the least.
Mainly adding Steel, Herald and Lady Argent as love interests. And then everything ballooned from there.
The option to remove Ricardo’s mustache was a surprise. Mustache gate was wild.
That so many people wanted to set their character’s height.
Other than that, so many little things. A lot of fun little scenes have been the direct result of a playtester going ‘man, I wish that I could…’
In short, enthusiastic playtesters are the best, and I owe them a lot. (Just has to know when to say no).
And I still am thankful for lady argent. Love a domme plus it’s going to be interesting when she learns our other secret. 
As many have written above… I have changed so much! I echo what @malinryden says about enthusiastic playtesters being the best, and how much I/we owe to them. I have added so many things due to people’s suggestions, and I continue to change things based on feedback. One of the beauties of IF is that you can add an extra scene or extra options based on what some people want, without preventing somebody else from reading the story in a different way.
Anyway, I also note that I don’t follow all advice (it would be too much…), but I do take time to consider every comment made, and whether it is possible or not to fit things… if it is possible and doesn’t take much time I always implement! Just, some things are more difficult or niche, or would take too much time (but even then, I often implement things just because it is fun, or an excellent idea, or I happen to be in the mood!)
Something non spoilery that I changed in Crème de la Crème based on tester feedback was including more specifics about the MC’s appearance. It’s not something I would have done off my own bat and I did quite a bit of internal back and forth over it, but ultimately came to the conclusion that my not being super into it didn’t outweigh how important it felt for some players. I didn’t go into as much appearance-specificity as some people would have preferred, but hopefully it was satisfying!
On the topic I wanted to recommend “Self-Editing for Fiction Writers” by Renni Browne and Dave King is an absolutely fantastic book. It covers many topics (from Show and Tell, to writing beats, to POV issues, to paragraph sizes)
In Choice of Rebels, I hadn’t expected anyone would want a romantic backstory with cousin Hector Keriatou. I was wrong. 
The desire to be a super-snobby noble (rather than a bleeding-heart one) shouldn’t have surprised me, but it did.
A few more can be found here.
Giving you feedback for the first game was a wild ride, Havie. You have a really good perk for Authors and it is you don’t take feedback as a personal attack. That is a defect so many authors have.
Criticism in one work is just that; It is not a criticism on one personality