My main gripe is with sloppy technique. A lot - not all, but a lot - of modern pixel art is purposely made to look overly blocky. Dithering and anti-aliasing just isn't utilized, which makes it look even chunkier than actual old game art does on a modern screen. It seems to me as if the artists are worried that classic pixel art techniques would make things look too good, though I personally believe the opposite applies.
I think a lot of this is due to where the nostalgia is being aimed. The number of pixelly games trying to look like a c64 or Amiga is vanishingly small compared to the number trying to look like an NES, SNES, or Genesis. (Or a PSX or N64.) And they’re mostly trying to make things like early first-party hits, not later third-party games that do crazy techniques. How many 8-bit-looking games sound like a Tim Follin soundtrack?
And of course given that those machines are from a generation that stopped being the new hotness about 30y ago, we have pro pixel artists who have never seen a game through a shitty connection to a TV unless they deliberately sought one out or had obsessively retro gaming parents; they just like making these square mosaics look like things.