Most will be VERY happy but those who live on their phone. . . .well some will never be happy.
I'm probably the latter :-D
iPhone performance when not on WiFi has always been rubbish for me and nowhere near the stated times from Apple.
iPhone 6 so far, day one after charging to 100% and running flat, mostly non-wifi with about an hour of WiFi.
Usage: 5 hours, 33 minutes.
Standby: 6 hours, 22 minutes.
I set up as new, loaded apps from iTunes on my MacBook, then charged to 100% before using it. So then starting setting things up, logging into apps, adding mail, etc..
Also had some Wifi usage in there (about an hour) downloading a few more apps.
Today, charged to 100% last night and unplugged. Woke to 97%
Currently on 61% after 3 hours 34 minutes. I'm projecting a total usage of just over 9 hours. That's on WiFi all day.
But as OP mentioned, early days with still setting it up.