I've had mine for just over a year now, T Mobile D851. It's been rooted, my only regrets are I didn't really need to root it, and it made updates a nightmare and I can't run hbo now with it rooted. But that's all about me rooting it - not about the phone, which is itself flawless.
The reason I rooted was I wanted to try to fix the screen appearance. However it turned out that you don't need root for that - I followed the instructions on fixing the screen contrast, and the phone was incredible after that.
I got in on the spare battery from LG, with the battery charger, which was all great. Super convenient when I had to fly. I have a 64GB card in it, so I haven't needed space. I have a bunch of vudu movies on there, for when I travel. Poweramp pro works great.
I can't really think of anything else. I have friends who got the iphone 6+ and I have no regrets, they all thought my lg was better.
I won't upgrade probably for another year - I don't see anything that is a big enough improvement to move away from this phone.
I'd like to unroot it, but I don't want to lose all my data. So rooting my phone was my 1 and only regret. Otherwise TWO BIG THUMBS UP.
EDIT: So I thought about this, looked online, downloaded the SuperSU from google play, and it worked like a charm. Unrooted! Even HBO Now works.