Bad pixel art is a pet peeve of mine. This is really advanced advice compared the problem most games have: - pixels of different sizes - rotating (!) pixels - scaling pixels - smooth gradients with millions of colours - dynamic lighting overlayed on top ... I could go on :(
There are two main categories of pixel art in games. In one category it’s about retro authenticity and these games are defined by the fact that their final buffer is the same low resolution as their art. They also often feature limited palettes, especially ones that were actually used on retro consoles. There’s also a second category of pixel art, where the style is more modern. The art is still low res, but the fina…
(Although I would consider a low-res limited-palette game which uses transparency, lighting, rotation, scaling and other transforms as retro since that was already possible decades ago.)
I (and many others) think mismatched pixel sizes look bad, but that there's nothing inherently wrong with those other things.