Hey there :3

So first of all, your terrain. I think it works, I like the shape, I like the organic-ness of it, and yes, that's a word now. I think what you could do is mix some other blocks in with the stone of the cliff, otherwise, it's just solid stone, which looks a little ordinary, especially for Ember! Same with the grass, except have more on it. Seen as I can see you've made a castle, maybe make some wheat fields around it, or a farm at least. As well, I think you need to add to the bottom of the cliff. Maybe build up the terrain a little bit down there, and also add some little details on the terrain (Like sugarcane, pumpkins, melons etc)

Secondly, your organics. I like the tree, but I think you need a few more of them. As well, I'd maybe add to the leaves, bring it out a little bit more. The leaves have a good shape so make sure you keep that element, just make it a little more bushy :3
What might also be a nice idea is to have something at the base of the cliff. Instead of the terrain idea, you could make some custom flowers or plants coming off the side of the cliff and leaning over the water, or going into the water, etc. Be creative! ^.^

Lastly, your structure. I like the idea a lot. I like the simplicity of the castle, but it's going to need more detail and depth. Your walls are all stonebrick, with nothing interesting on them. I can see you've made it like a destroyed castle in some areas, but to me that just seems like an easy way out of detailing and making structure, because it means you can just randomly place stuff and say it's a broken building.
I think in one or two places, this is okay. But don't make it the entire concept. You're going to need to detail the castle more than this, with a few layers of depth. Have a fly around and look at how others have made castles and you'll see. A lot of the time, they start with pillars, then build and detail off of them.
Lastly, to fit with the castle theme, why not build something like stocks? Or something medieval to fill some of the empty spaces on the terrain. Also, loving the bridge! :3

Good luck!
- Dutty :3