Hey there!

Firstly, terrain. I like the different types of terrain you have - the grass gradient to the sand. I think there's some areas on the sand terrain that are too flat - you could add some layers to the corners like you have with the grass, just to make it less flat adding more depth to the terrain there.

Secondly, organics. I like the tree. The trunk could be a little thicker at the bottom, and the leaves could be less square, but other than that, it's a nice tree.
What I think you should add, organics wise, is custom cactuses. They look so much nicer than Vanilla ones - here's my design:
http://i.imgur.com/1OTGJJ9.png
You're quite welcome to take from it and make it your own.

Lastly, structure. Every plot needs some for of structure on it. I like the underground area with the buried body and the Lore. It's all very fun when plots have things like that.
That being said, you are going to need a form of structure above ground. To fit with the Lore of your plot, maybe you could make something like a Mausoleum - made out of stone/stonebrick. It's basically a tomb, but you can detail it and make it all nice :3

Good luck!
- Dutty :3