Overall, I am quite satisfied. I was the same with iOS 15, 14 and 13. Dark Mode was what I mainly missed, pre iOS 13. My wishes are just "nice to have" and they are not in a prioritized order.
1. Possibility to change the notification sound on 3rd party apps (not all apps support changing the notification sound)
2. Option to reset "Life Time" in the Mobile Data menu
3. Option to customize the App Library
4. Ability to edit title, album and artist in Apple Music directly in iOS.
5. This one is controversial. A button that can close all apps at once. I know it doesn't benefit the battery, but still. I also think that a lot of people who help their grandparents with their iPhones would appreciate this feature. If Apple is afraid that people will close their apps all the time, and thus experience bad battery life. Then the button can appear when, for example, there are 20+ apps open.
6. Option to install 3rd party apps (can't wait for them to open here in the EU)
7. Option to change the shortcuts on the Lock screen. I want a shortcut to my Ring Camera and my driver's license app.
8. Live view of who is writing in the status bar, just like TypeStatus in the good old Jailbreak days. I don't think Apple will ever release this feature.
9. Better battery management. Option to stop charging at 80%, instead of the phone having to learn my pattern itself.
10. The option to delete previously downloaded apps from the App Store. Not just hide, but completely remove the connection between the individual app and one's Apple ID. This is possible in the Google Playstore, I don't think it's all science fiction.
11. Option to remove previous subscriptions that are no longer active. Again, not hidden - removed completely.
12. Private Relay throughout iOS, and not just in Safari.