I've been using the LG v10 for about a day so far, an upgrade from my HTC One m7 GPe.
Overall, it's a nice device. A bit big, but I should be able to get used to that since I used to have the first gen Galaxy Note.
The UI is a little different... In the app drawer, there is a Google subfolder. You can add additional apps to it, but can't sort them. Actually doesn't look like you can remove them either. Haven't found any way to add additional folders yet. I was able to hide all the AT&T bloatware, so that's something.
Second screen? Eh still haven't decided if it is gimmick or useful. I didn't buy it for that feature anyway.
I was going to replace the launcher with the Google Now launcher, but I like that it is a doubly linked list so I'll keep it for now.
I do like that there it's a dedicated button for screenshots - the HTC was notorious for making me try try again. I also like that I can change the soft buttons ( order and content ).
I do not like the buttons on the back. I'm sure I'll get used to them, but whoever thought it was a good idea to encourage people to accidentally put their finger on the camera lens repeatedly was obviously not a photo buff.
I haven't run any cpu or ui benchmarks yet, but it seems rather quick. Speedtest wasn't looking great. Time will tell.
And in case you are wondering why I went with this phone, it was mostly because I wanted to try out the manual camera mode. I don't expect it to beat out my Canon, but it seemed i interesting. Also, removable battery and sd are hard to come by these days.