So I've has mine for about an hour and a half now and finally managed to get it all set up (twice) with a restore from my 5S, put 9.1 beta on it (because I wasn't sure if I had to to restore from my 5S), get all my apps, pair my watch and finally have a little play around.
First impressions - 3D Touch is a gimmick but an extremely useful one at that, that will likely grow on me for making quick phone calls. The screen and live wallpapers are simply stunning, I've gone for the blue smoke as fish aren't really my thing. Touch ID is impossibly quick, my 5S took a good few attempts and about a month of learning my finger to respond well but the 6S+ has been set up very quickly and sometimes I'm not even convinced I've touched it.
I genuinely didn't realise that a Plus model was quite this big, even though I've held one in the Apple store, but I do still love it. 2 handed use is no big issue and I already hate the feel of my 5S, wayy to small. Can't wait to use this phone for the next year or two.