It looks great. One thing I don't like is the stock camera app have auto focusing disabled for videos, and the third party apps doesn't support 4K for it.
I would consider getting the Nexus 6 if it take videos as good as this considering it uses the same sensor, but also have hardware image stabilization.
For the OnePlus, if you use the stock Cyanogen camera (not CameraNext from CM11S), it lets you turn on software image stabilization, and it have auto focus too, but no 4K option.