One of the things that keeps getting me is, exactly how is the player supposed to be interacting with this map? Should you be able to see little people walking around, or little trucks or wagons roaming around? If that's the case then the view is simply pulled back too far. Even if the player is just selecting large blocks of land to be mining, I'm wondering if something is supposed to be shown to the player, like a little road that gets built to the mining site, or little buildings or equipment.
Honestly, you should start with those kind of elements. Because right now, we are really missing a sense of scale. That river could be half a mile wide or some tiny creek. Are those rocks or hills or mountains? Are those trees at the bottom, or sage brush? If a person was walking around here, would they be too small to be seen? I really have no sense of scale, and if you're making an actual game and not just some art, that's going to bite you down the road.
So try drawing some of the things the player is going to use when they interact with the map, and add a few items or landmarks to help establish your sense of scale.
After that, well it's hard to be specific since I'm not sure how big any of these things are, but there is a lot of uniformity in the width of that river. Take a look at
this image I found. A river looks more natural if it has more variety in how wide it gets.
And unless those are rocks just sitting on the ground, then those mountains don't blend in well. Mountains don't just pop up on the plains, they form ranges. It makes them a lot trickier to draw, especially if you want to reduce the number of tiles you are using, but if you want good art you have to put in a lot effort. It's just the way of things.
The angle you are using is also making this a little tough. The mountains themselves look like they are being viewed directly from the side, but then everything is arranged like you are looking directly overhead. Try to imagine everything from a slanted angle. Look at some isometric art; do a google search for isometric desert and isometric mountain. You don't have to actually build the game in an isometric format (although that would be suggested if you want a more 3D looking map) but natural things like mountains and rivers and trees look the same from an isometric view as they do in a tilted view, so those kind of samples should give you some really good ideas of how you want them to look.
Here's a good one.And finally, vegetation tends to grow in predictable spots in a desert. Near rivers, and in basins where the water collects, and wherever the runoff from the mountains would gather. Keep that in mind. Add some greenery near the river and in the flat areas near the mountains.
