Got my iPhone 6s yesterday. Haven't played around with it much yet, but a few observations:
This thing is rough ridin' huge compared to my old 4s. I like having a bigger screen to look at, but it's really uncomfortable to hold. Typing is a two handed operation now.
I hate the rounded edges. I guess they rounded them off to make it look slimmer from the sides, but it makes this phone one slippery little bastard to hold. I ordered a case which hopefully bulk up the edges a bit and make it easier to hold. The squared off edges of the 4s were much better.
Battery life is good. Haven't charged all day.
The included "health" app is pretty neat - tracks your movement like a Fitbit - but obviously only works if you're always carrying your phone.
As expected for an apple device, this thing is FAST and oily slick when swiping pages, opening apps, etc. the iOS is really nice.