Is this really pixel art? Because I think there are too many shades for the colors. I don't want to zoom in any further just to confirm this it should be visible from the very beginning.
I really feel you!
The approach of creating pixelesque textures in a different way than the original shows that he is clearly not aware of what he is doing!
Overall, in that current state, to give it a more pixel-like feel, you'd be better off with using plain colors and not gratients that are barely visible to the eye, because the current shades give it a feel of an artifactized screenshot of a game! For really really basic tileable rock repitatives I suggest look at early Gameboy games or GBC! As for the character, use plain white, to make it more visible and seperate it from background and evironment, as it is without a doubt the main focus of the entire game (if it's meant to be one)
As for the cave, the overwhelming gradients don't really work in favor of ambience! Aswell as the brutally different geometrical contraticting shapes (good contrast, but used wrong!)
-For a beginner it is not that bad and could technically work out, but from a visionally point of view, it could need some more things to go together bound by certain rules to make it not as messy-
Don't make yourself life harder than it is, if you want to place nuances/accents, do it differently but not with such misused gradients!