my biggest ask would be for custom colour themes? And maybe a one-time paid app to avoid any future ads (if you are thinking of going down that road). An app or a game with ads and no way to pay my way out of them is an instant uninstall.
Someone in another comment mentioned that they do a timed challenge with friends. This would require signup etc. Even though I sometimes do a race against my son I'd probably not sign up/register just to do this. But if it's purely optional then I think there is some merit there and people who are signup happy may take advantage.
I may also like to see perhaps a second (premium) daily challenge. Not unlimited mode because that would just make me gorge on it and get fed up. But two daily challenges instead of 1 might be something to ponder. Maybe even for a small pay? Just don't make it obnoxious with nags and popups etc.
These are fun ideas!
The custom color theme is really interesting. Are there specific things you'd like to do with the custom color theme? That seems like a fun feature to build.
Having a second daily challenge would be great, but a lot of work. When I launch player puzzles I'm hoping to roll some of those out along with the daily puzzle so that on certain days you get a "bonus player puzzle!"
On custom colour themes. I have no good ideas. I just know when I like a theme and when I don't. The deafaults in the game, are.... not great for me. Especially the light theme (I generally prefer light themes). I use the dark theme in the game now because light is not that great but dark is also a bit ho hum. So maybe a theme store would be good? A buck a theme or something? I'd rather not do theme imports etc. Too much work and I don't know what I'd like. I'd rather just swipe through a bunch of themes and hit "buy/pick" when I find one I enjoy. That's all.
One small feature I'd propose is that maybe you want to have a "hard mode" baked in where no hints are available? I personally do not use hints to solve the puzzles. I can usually piece everything together just with what's on the board and the word descriptions and never reach for hints. Hints feel a bit like a cop out so I avoid them. Maybe having this as a different game mode is a good idea? I'm not sure - it depends on the complexity of your implementation of you want to create a feature flag or not.
Great feedback, thanks!