Context: I bought and retuned multiple monitors in the last few months looking for a monitor without major issues, I went through 5 AOC 24G2, they all came with dead pixels, I then tried an Acer XZ242Q and it was just plain bad, with sharpness issues and non funcional G-Sync. Finally I decided to spend a little extra on a Dell monitor with a TN panel even though people sway you away from TN at any chance they get.
My initial impressions of the Dell S2421HGF are very good!
Build quality is better than other options in this price range (but stand lacks some axis). Image quality is very decent, much better than the Acer XZ242Q and only slightly more muted than the AOC 24G2, backlight bleed is minimal and the screen surface is a little more on the grainy side but nothing that bothers me.
I can only conclude that the guy who reviewed this monitor for Tom's Guide is clueless, when using one of the custom user profiles (Game 1 to 3) the monitor gives you access to a whole bunch of settings to mess with, like saturation, hue and gain controls for individual RGBCMY channels, that's the best OSD flexibility I've seen yet.
Pixel response seems to be great but I lack the means to test it non subjectively, even when setting overdrive to its maximum - called extreme - there's no visible overshoot when using G-Sync with the range of 64-144hz (not tested with G-Sync off, Dell's overdrive seems to change its behaviour when G-Sync is off).
G-Sync works perfectly with only a minor issue which is it blanking for a second when the fps dips below 49, probably an issue only on GTX 10 series cards as pcmonitors.info mentioned.
The AOC 24G2 is a bit better and a bit cheaper, but is only worth it if you get a PERFECT unit, which in 5 tries I hadn't.
I was wrong to rule out these new TN panels in favour of these cheap IPS ones, the S2421HGF is fast, clear and vibrant.