Hi there, I am definitely no expert, but this is my opinion.
I feel that for this artwork, you did both a few things well and a few things a little worse than usual.
Firstly, I'll start with the negatives. On the left hand side on the image, the castle doesn't actually seem to fit in too well, I'm guessing it could be due to the photo used. The colour is correct, but seeing the texture of the cliff makes the scale feel off. I think it could be the contrast of the scale that makes it look a little weird, for instance the right hand side looks farther away, furthermore the deer makes it look closer but the left hand side doesn't seem to fit properly with the other parts of the image.
Next, the cliff itself seems cut out rather than actually in the image, maybe it is due to the few stray protrusions near the waterfall, either way, it doesn't seem blended in as well as you usually do it.
Lastly, the scale for the waterfall itself feels off, I'm not too sure why, maybe it's the portrayal of the waterfall next to the castle which should be far in the distance, and thus the waterfall may look too textured for how far it is supposed to be away. I guess I might just be nitpicking.
As for the positives, I loved the way you used the right hand side of the image to show the scale of the image. It does really give a sense of majesty, a large cliff face.
The use of the mountains in the distance are also well done, giving a very mystical feel and a great sense to the overall atmosphere of the piece. The use of the cresent shaped reflection of light on the planet really gives that dark atmosphere.
In combination with the above, the type of clouds used are also perfect for this type of image. I guess all in all, even with what I see as the negatives it's still beautiful to look at and is definitely well done! Keep up the good work!