Power guzzling iOS11
The biggest problem with iOS 11 is the power guzzling. My iPad Mini 2 used to last 8-10 hours but since updating it only lasts 4-6 hours now. Annoyingly my iPad 2 is incompatible with any iOS since version 9.3.5 yet it still works perfectly. As usual with Apple they build obsolescence into their products to force you to upgrade to a newer phone and iPad. The good thing with Apple is they don't charge you for it, so that's a bonus over other systems.
As far as the comments saying they're too expensive goes, so are their rivals. Samsung phones are on a par with Apple but spend more advertising how marvellous they are and yet they still use awful Android; I say awful because it is unless you're used to using a Spectrum 48 and don't want to use anything more complicated.