I hate to say this but, you still have a lot to learn. There a few problems that need addressing here:

1. The colours are pretty poorly picked, they are far too saturated and seen to convey a cartoony atmosphere (if that what you are going for then great!). Your dirt does not look like dirt, it is too green and the colour is too simillar to the rock (in my opinion the rock should be an off-grey). You should also try changing the hue in your colours, shifting towards purple for shadow and yello for highlights. colour can bring a lot to any pixel piece.

2. Detail. There is not much detail in this work, the rock is very flat and does not have any imperfections, this makes it boring to look at. The clouds are also very plain, try adding some reflections and such.

3. Shading. There is a lack of shading in this piece, there needs to be shading where the grass meets the dirt as well as shading where the rune meets the grass. the little bits of rock in the dirt should have shading where it meets the dirt as well. I would suggest using dithering on the rune, it would make it look less flat and more interesting to look at.

4. Contrast. Contrast. Contrast. This piece lacks it. without contrast your work looks very flat, speciality the main focus, the rune. I also did not notice the rocks in the dirt before i zoomed in on paint.net to have a closer look.

I hope you listen to my advice and try to improve upon your work! :D