Maybe I am a little on the geeky side, but this has been the most useful iOS update I've ever installed, and the reasons aren't geeky at all...
1) Family-tied Apple ID support. !!! !!! !!! We had previously shared all our communal apps and music by having the "two devices - one apple id" method, but that meant that all cloudy things needed to be carefully disabled lest our mail and texts start leaking between devices. Now we all have separate apple IDs tied to the same account and content, and EVERYTHING WORKS. It was worth installing iOS 8 (three times!) for this feature alone.
2) Better app integration. I'm already noticing this in several places, particularly photo-manglers being more easily accessible to and from the camera and LastPass working more closely with Safari. Sure trying to explain what they did for developers sounds ridiculously geeky, but the effect is that activities that seemed awkward now just work, which any user can appreciate.
3) Messaging typeahead changes. I actually like the new "suggestion" UI and have found it loads easier for both shortcutting typing when it guesses correctly and for cancelling an upcoming "correction" that I don't want. Since my wife seems to communicate almost exclusively through SMS these days, this is a godsend.