Terrain is quite bad to be honest but there are ways to improve this.
First, there is a waterfall but no water source like where is the water coming from and falling at (I am sure that it has no water source though not sure if it is falling on a water not only shown in screenshot or simply there is none)? You should connect it with a body of water. You could also better use Raise tool to raise ground and make some high platforms instead of Blizzard Cliffs but no grudges to cliffs. Terrain also lacks variations, ground is flat in the platform and could have some combination of tile uses instead of just plainly Grass and Rock Tiles. Trees could be a little bit raised for they look small and lastly, you could add some fogs into it.
Practice and practice and you will be a great terrainer someday!