It is very basic, good idea, but it has way too much empty space. Which is especially bad for a huge an seek map. The caves don't look that natural, they need to have better curves and why are they stone I they are in the end? The terraforming is very flat, and too humdrum. I would recommend adding a few blocks such as sand, birch, or sandstone to help the color pallet. Good luck.
My exact thoughts, never use pixel art, always organics, and make the terraforming more interesting and not as plain.Hmm... I like the idea, but you should try to make the giant Enderman and Eyes of Ender more organic and 3D instead of like pixel art. I'd also make the caves more detailed, with more passageways and openings if I were you.