I need criticism of what needs to be fixed/added, help! 
Vines on the walls?
A little water source. (ICE)
And some of the trooper’s equipment that he might have on the floor behind him.
Non-default lighting.
Since dynamic lighting came out, GlobalShadows is the default.
It makes me feel like I’m thrown back in age. Might be what you want - though I’d suggest that you tried smooth terrain. Especially because it’s a natural structure, and not human-created.
You could enhance the crystals using Neon to give it a faint glow. 
As from there on, I don’t know what can be fixed/added. Just throw a link to the game when it’s done 
Isn’t that the map for devWes’s and samaxis’s Glacier-238U?
How do I use neon on bricks? :0
I used their style to base the environment on the 2nd star wars movie, I didn’t copy/paste.
Its a material, just go to the object’s properties and change the material from “Ice” to “Neon”.
Also I’m curious, is the thumbnail supposed to look adventurous as if the clone trooper is looking into a distance. Got a positive " hero" feeling to it almost. Reason why I’m asking is because I don’t know what type of game it is meant to be. Let’s say it is a war game or a hunting game, then you want to show some weaponry and equipment that the soldier/hunter use. Possibly even a vehicle of some sort, looks like a snowy distant place so maybe a snow-scooter?
Or if it is a mining game for example, then you want to show some of that equipment mixed with some character full of joy because he has found some great treasure sealed away deep in the earth.
What I’m trying to say is that it kinda depends on what type of game you are working on, so more info pls.