Same here. I had bought my 6s after my 6 got stolen, so it was my first time using iOS 11. My two-day old phone was absolutely unusable, freezing for over a minute every once in a while. Apps wouldn't open at all! I couldn't change the volume while the phone was locked. I couldn't listen to musics, or use the lock screen music handler, while the phone was locked.

You have something really wrong when your smartphone can't open apps...

After one week I got tired of this shit and downgraded to iOS 10, which for now is working as expected. I really hope apple won't force me to update to iOS 11. (So here's what I did: I intentionally filled my phone space. Good luck fitting iOS' 1GB here).

Frustrated disappointed and utterly angry at Apple. This is definitely the last iPhone I'll own.