Pixelated sprites, but also complex material shaders on the walls and directional lights and ambient occlusion and HDR and...
This is one of the main things I hate about the "boomer shooter" (vomit-inducing name, I hate it so much) trend. They can't decide if they want to imitate a software renderer, shitty opengl hardware renderer, or some unholy mixture of the two. So they end up with this weird aesthetic that looks like a video game you'd see being played in the background of NCIS or some shit.
Some of my "favorite" examples:
STRAFE (even though I love this one to bits in spite of it):
Beyond Citadel (some weird Japanese freak's anime guro fetish game that looks like a shitty unfinished prototype, but is a game you can buy for 15 USD right now. Sitting at Overwhelmingly Positive):
CULTIC (every screenshot of this game that I see represents a complete lack of any ability to frame a scene. Everything muddles together so bad. Can you tell at a first glance that this takes place in a forest?):
Exophobia: 8x8 and 16x16 textures, plus default Unity volumetric fog to hackily mask the fact that there's no lighting or vertex shading so the entire room would cludge together without it):
Generally there seems to be this belief among retro-style games that retro means intentionally making the game look like shit. But you can go back and play Doom or Wolf3D or Marathon and see that those games, while obviously dated, did a lot within the confines of their aesthetic. There are some levels in the original Doom that make beautiful scenes with tons of personality just with sector lighting on a software renderer.
There are games that can mix modern graphics techniques with retro styled stuff to make a great aesthetic (Dusk, Amid Evil, etc.), but in those cases it's always done tastefully and carefully and not "oops I left a default setting in my game engine on."