Hey there! :3

Firstly, terrain. I really like it, you have some good diversity and a nice palette. The whole area at the base of the cliff is way too flat though. You could easily have more layers than two! It'll add to the atmosphere as well, and make it less bland. You should also 'decorate' the grass areas with grass, flowers, wheat etc - it adds more atmosphere and also makes it look prettier! :3

Secondly, organics. Your trees are really nice, but better roots are needed on the grounded tree. The leaves are nice - you have a good percentage of air, and a nice palette for the leaves! You could have some smaller trees around, not only the large ones, to add to the atmosphere.
Your dragons are okay, however a little chunky. They need some definite curves! It's too squared off on the body and the legs. The wings also need a lot of work. I wouldn't use a solid block for the wings, especially not the same as the body block. Seek out one of the organics build team members (WZStripes, Rudim, IceRock etc)

Lastly, structure. You only have one structure on your plot. As it is large, it's a good use of space, but you will definitely need more structures around the plot. As you have dragons, maybe you could have a destroyed/burning village? Medieval in style, to fit with the castle.
The castle itself needs way more detail! Your walls are too flat. You have a really nice design for the building itself, and I like the contrast of the blue windows with the andesite, which I've never seen before! But either way, more detailing on the walls! Stairs, slabs, just not too many!

Good luck!
- Dutty :3