This screen can't really be judged at it's full potential until we get 4k@120Hz with Gsync/Freesync. It'll be close to Xmas by the time I've managed to evaluate that, and even then, if new GPU prices are too high then I won't bother.
I'm happy to play 3rd person at 4k with reduced settings to maintain 60fps, but I'm not enjoying 1st person as I play them with K&M and that requires higher frame rates, especially on a screen so large/close. Dropping to 1440@120Hz only works with some titles as it can look washed out on others.
I know this is a PC forum, but I have to say I'm enjoying 4k HDR content from Amazon & Netflix - the availability has really improved big time. I'm finding it difficult to watch HD content now that I've seen the 4k stuff at it's full potential. That's a big reason I went for this screen, it's a terrific all rounder in terms of gaming and video content.
Anyway, just some Nightshift rambling.