David Pierce, writing for Wired:

That’s when I noticed the difference between the Pencil and just a stylus: It felt great. Perfect. Better than any stylus I’ve ever used by a wide margin. Not because the thing itself is so terrific—I like holding FiftyThree’s Pencil better, and there are lots of good styli out there—but because it’s the first time I’ve ever written on a screen and actually felt like I was writing on the screen. There was almost zero latency, meaning the ink appeared to flow out of the Pencil and not trail half an inch behind. With the tiniest added pressure, the line became the tiniest bit thicker. I tapped on the No. 2 pencil mode, and it wrote and shaded just like all the pencils I used to sharpen with that wall-mounted thing you had to crank.

It’s all about the latency. Make the latency disappear and then developers can really go to town.