Its not bad.
I've got some feedback if you'd like it and a paint over I did.
The scene feels very flat this is mainly because the lighting is not well defined additionally you should focus on the form a bit more. you'll see what I mean in the paint over.
Its all rather blurry, It appears you applied liberal use of the smudge tool. Thats fine for working the base values in but you really need to go back over it with sharper details. I don't mean cracks and stuff but you need to define the shapes and form. These are rocks, if this cave was made of flesh then it would look fine (more or less).
If you are gonna be using hd resolutions then you should take advantage of all those pixels so some finer details will really push the look. In the paint over I simple did filter render clouds, and then filter spatter or something. overlay that onto the rock and instant detail. (you should do some finer hand painted details as well tho).
Last thing I can think of is you should darken (or lighten depends on the situation) the objects as they get further away. This way you'll get a much better perception of distance mixed with parallaxing and it will look awesome.
And heres the paintover, its not perfect but you can see what I mean about defining the form to create a more 3 dimensional look. If you start out by drawing cubes and cylinders then go over that with rough values it will really help you.