Higher cave, have something in the distance aswell that is hard to see but that you can see just a bit, as it looks like this just stops right there and that is the end of the world.
Also you need to add some shrubs and other things around the root of your trees as it seems very empty and Blizzard trees doesn't look very good on their own without any shrubbery.
As Pyritie mentioned the fog should be adjusted to fit the sky or the other way around.
I don't think the ground itself needs any height variation, it looks good as it is. Also your use of doodads leeding up to the cave looks very good, the hanging corpse fits in perfectly, you've done a good job there.
Now to the cave itself the entrance looks great but the torches seems to be hanging out in thin air? That does not look very good, either make it more obvious if it is meant that they should be attached to the wall or else place them on the ground.
If you improve on what I and some of the others has pointed out here then your piece should end up great. Just keep working on it.
+rep.
EDIT: And congratulations on receiving your second rep bar