Hey there!

So first of all, I think you should build some terrain - http://www.reverieinteractive.com/BetaGames/Minecraft_Clone/MCCloneTech1.PNG - something simple like this shows good depth in layers. You can make it a lot less layers and smoother than this, it's only an example.

Secondly, your organics. I can see you have a small dragon build. It's really cute - if it made sense on the plot, maybe it'd be acceptable, but it's a little random. The most common kind of organic is usually a tree. Maybe this'd fit better on the plot :3

Lastly, your structure. It's a little too simple. The wall design on the side of the castle/tower has no shape to it, it's all one block kind and has no design/detail/depth at all. On the top, you've clearly shown that you can create shapes and nice design - use this on a building design.

Good luck!
- Dutty :3