After years of working with a secondhand Intuos II, I finally had the cash to buy a brand new Wacom Cintiq 13HD. However, when setting it up, I noticed that the screen area was tiny and a little blurry despite being set to max resolution. A lot of poking later, I found that Windows 10 had decided that I needed a 150% zoom in the Display Settings. Resetting that to 100% fixed the issue completely.
So, for those Google searches out there: Blurry Wacom Cintiq 13HD Windows 10 Fix Display Settings "Change the size of text, apps, and other items" to 100%
...And now to go colour something.