I have a Dell XPS15 with the QHD screen. It's a fabulous screen, rich, detailed, curves are displayed smoothly. My *perception* is that it's more pleasing than an Apple retina screen, based on owning a (non-retina) Macbook and seeing little difference between that and a Retina screen at normal working distance, while the screen in the Dell seems much more pleasing.
The downsides:
The fine dot pitch makes images displayed 1:1 relatively small if you need to pixel-peep (to check sharpness etc) and can make images seem a bit better than they really are.
Despite being IPS, there is some colour & brightness change when altering viewing angle just a few degrees. It's not huge, and if you were not looking for it then you'd never know.