Variable refresh rate
It really is an absolute game changer, especially at settings where your GPU can't get you up above 60 FPS.
In case you aren't sure that you've chose right (though looks good to me), have you seen these?
of monitors is short because although it now does FreeSync in the latest drivers, it's only turned on by default in the (few) monitors that NVIDIA staff have certified, this is the 'G-SYNC Compatible' group on the page. These are typically much cheaper than the full 'G-SYNC' monitors which require expensive additional (in-monitor) hardware. Others, like my BenQ XL2730Z, could well be very good screens with wide VRR ranges (e.g. 40-144 Hz) but not be certified to work when you tick the box in the NVIDIA control panel.
is much bigger, and actually helpful in finding a monitor to buy; these should all work on a recent GeForce once the box is ticked, but it's not guaranteed.
Blur Busters' list
is at least independent, and is split into groups so you could find see the high refresh (also game-changing IMO!) ultrawides all together.
Desktop: E3-1270 v5, X11SAT-F, 32GB, RX Vega 56, 500GB Crucial P1, 2TB Ultrastar, Xonar DGX, XL2730Z + G2420HDB
HTPC: i5-2500K, DH67GD, 6GB, RX 580, 250GB MX500, 1.5TB Barracuda