Super Mario Bros custom tileset

[Gors]

and here's where your true ability starts to show

You are still scribbling. Don't do that and call it a day. Clean it, don't leave outline pixels so crudely laid out like that, it is terrible. Blocks should not be shaded with a curve on the bottom right corner. This only occurs when the object is a ball, or has a beveled surface like a button. Blocks obviously don't fall into these categories.

You're just gradient shading, without taking shape and depth into account. Go look for references on how others shade blocks and rocky surfaces, and pick better colors for the cave tileset. They're really saturated and reeks of MS Paint. Same with Lava.