I did a throughout screen test on mine and found no major issues. Uniformity is not perfect but higher than I expected. Close to no backlight bleeding which is nice. Gradient smoothness is quite good (8bit dithered to 10bit simulation is true). Peak brightness is more than I need for calibrated print/photo work. Dark area contrast is not the best but workable. I have a distaste in glossy coating in general but they did a good job with the anti-glare on this one, if I control my ambient light in the room there is close to no noticeable reflection. And due to being glossy the contrast and viewing angles are a bit more consistent than the matte Dell that I set next to it.
I have used many Apple branded displays and iMacs before, this one is easily the best out of its own crop. Compared to likes of Eizo and NEC it is very high up there, if only it had more hardware calibration and controls. But for what I paid with a nicely spec'd mac along with the monitor I am more than happy with it.
*** only one minor problem: the factory default is D65 white point but I found it more yellow than it should be. This is easily offset by 3rd party calibration but not as much with ColorSync Utility.