The images don't correlate to the x-axis perfectly.
I don't think it's a good idea. Will confuse a lot of people, who stumble on this graph by chance. I'd certainly make examples more emphasized to illustrate the point behind this. Eastward and Superbrothers are both very much traditional pixel games, despite having non-pixel effects and lightning on top. Dan Fessler's squirrel mockup is a classic example as well, and should be somewhere in the middle I think. By the way, where does this sample with red mountains and blue forest comes from?
While I was much more of a purist before, now I'm leaning on "whatever makes you tick", which corresponds to broad definition by this chart. I'm still relying on good ol'
"caring about individual pixels" definition. Also palette conservation, but in my book "caring" does include this as well. Opinions on border of these will differ from person to person.
On the
left side my prime example is Slain! Personally I don't consider it pixel art, though quiet expectedly many will. It's digital art made with hard brushes, so it heavily resembles pixel art. Some sprites are pre-rendered low-poly models. Don't get me wrong, it looks cool.
Index painting would certainly be on the far
right side, borderline with digital painting. The real difference is palette conservation, though this border is blurred. How many colors are too many?
Many of modern point-n-click adventures have pixel sprites and low-fi non-pixel backgrounds, that I'll probably put outside borderline definition. But they look pixelated and
blurry rather than pixelated and
noisy, so I'm not sure about them. Guess they are closer to digital art on the
right side?
Most of pixel graphics are made for game projects. I think it's not the purist definition that matter in this case, but rather question "why pixel art?"
Cheap could be a perfectly reasonable answer, nothing wrong with that.
Nostalgia is also fine. But for me it would be
crispness or
sharpness. Good palette and color conservation make image pleasant to look at. While crispness not only makes everything very readable, but can also have noticable effect on gameplay, especially in action games. That's why I tend to dislike games that look very muddy and use many shades of grey, but very much attracted to any Nitrome games, since they all look super sharp and perfectly readable, even when scaling and rotating sprites. That's what attracts me to pixel-based games, and in my eyes is one of the main strengths of the medium. Making muddy pixels can convey a certain dirty effect, but I'm not a fan.