So far I’m really digging iOS 11 on my iPad Pro (12.9” original version) and my iPhone 6.
My iPhone 6 performance seemed like it took a nose-dive about six months ago, and I was puzzled because I couldn’t tie it to any specific update. It wasn’t right after any iOS point releases, certainly wasn’t back when I updated to iOS 10. But it had me worried for the worst, that if it was already chugging on 10, 11 would kill it.
In fact, fingers-crossed, I’ve found 11 to be an improvement. I think it’s mostly due to some tweaks to animations and transitions. I doubt there’s much—if anything—in the way of actual performance optimizations. But from fearing things actually getting worse, a perception of slight improvement is exciting!
On the iPad, I have no idea how you’re supposed to learn some of the new multi-tasking gestures on your own. There’s a lot of room for improvement in education and more intuitive feedback to get you going. But once I started to get the hang of it, I really liked it.
Viticci’s massive “review” has been very helpful in that regard. https://www.macstories.net/stories/ios-11-the-macstories-review/17/#content