colours seem a bit dull I'd try experimenting with colour and contrast, and I don't think the dither really works in most the instances used and alot of those black outlines seem really harsh, and in your dirt tiles in particular the additional colours don't add much to it, just make it look noisy, rock wall tiles have some strong shapes that are easily noticeable and make the tiles look very repetitive
I'd suggest working on that tile a bit more too, try to make all the edges and shapes rather consistent, right now there are some strong shapes that are larger than others so maybe split it up a bit, if you can't make it tile well add a secondary alternating tile to lessen the effects that are reinforcing the grid, here are some quick suggestions
keep working they definitely capture a retro feel so far very NES Final Fantasy-esque
also just noticed the characters, 3rd frame in on the side on frames, you should separate the hand face and leg, at the moment it looks like they suddenly have beards, or walking sticks
