The rocks in the upper left area look very blurry as if they were resized.
Out of habit I had set the tile sizes to be 16x16 as opposed to 32x32.

I later realized my mistake and resized the image, the side effect of which was that everything became very blurred. I definitely need to fix this, and I'm tempted to completely redo those particular rocks to fix the lighting problems there as well.
What exactly is the grey and yellow arc supposed to be? A piece of metal junk?
I had intended it to be an old arch that had sort of fused together over time, but I don't think it turned out quite the way I wanted it to... perhaps I should add highlights to emphasize each segment, or darken the lines separating them?
The lineart you drew looks good but not very tileable. Good tilesets should be based on segments which can be combined in multiple ways to create any shape the mapper wants.
The rest of the structure is just a placeholder for the sand/brick style done so far, and should be completely replaced by the end. I was intending to have the outer walls as one-off tiles, only used once on one map, so I hadn't taken tileability into account when drawing them...
The sand texture in the lower left looks very good.
Thanks!
---Freeyorp