Hey there! :3

Firstly, terrain. You have nice terrain, interesting block type using the mycellium (or however it's called!), and I like the variation you have in layers. Looking good! What you could do, so that it doesn't all just look like plain floor, is 'decorate' the land a little more. Mix some dirt in with the block, maybe, and also have some mushrooms here and there!:3

Secondly, organics. Your trees are alright, just a little basic. They also all look the same, so you could include some that are a little larger, or maybe some hedges (like only leaves in some areas of the terrain)

Lastly, structure. You have okay structure, but its a little simple to rank right now. You haven't really shown much use of detail/depth in your structure, but you could make the centrepiece have some more detailing - make it a little larger, add some stair/slab detail etc, using more block types that what you have already!
I like the underground area, but you could also detail the walls down there too, as they are a bit flat! ^.^

Good luck!
- Dutty :3