I've had the AW3821DW now for a couple of weeks now. Really pleased with it, came from a pair of U2412M monitors so it's quite a jump to ultrawide with G-Sync and HDR. Paired with a 2080 which seems able to drive most games reasonably well, sometimes need to drop some of the settings down.
I've calibrated mine using an i1 Display Pro + DisplayCAL (D6500 white point, 120cd/m2), these are the custom colour settings for comparison:
Red: 100%
Green: 97%
Blue: 88%
Brightness: 22%, Contrast: 75%
You can see that I had to dial out quite a lot more blue than others to get to D6500, using defaults it was reading just under D6900, but I appreciate most folks probably prefer the more blue white which is probably why Dell default to that.
I actually found the default icc profile provided from Dell's website was pretty accurate, with a maximum delta errors of 1.3%/average 0.4% when using the above settings. Using the profile generated by DisplayCAL maximum delta error is 0.93%/average 0.35% which is excellent. These measurements are using the Display Pro, so in truth differences will be below the error tolerances of the device anyway, unfortunately I don't have a spectrometer to get more accurate readings.
Haven't used the HDR mode much yet, I did play a few YouTube videos which look pretty impressive but the non-defeatable backlight dimming and lack of brightness control is annoying, so I can't see myself using it very much.