Going from left to right:
#1. That is a freakin' awesome cave. Looks like it would scare the living crap out of me to walk down it. Very good.
#2. Rather plain, but I do like the lighting and the river at the far end. Pretty cool.
#3. Absolutely beautiful (yes, I know, everything there is dead) forest. I love it.
#4. I really hate the purple mist and the trees. Ugh.
#5. What the hell is that?
#6. I can has that map? Seriously, that's freaking awesome. I love how it looks totally poisoned and the destroyed house there.
#7. I don't really like the terrain itself, but the sky is pretty cool.
#8. WHOA!!! That moonlit cavern with that little tomb is freakin' great. 5/5.
#9. Rather plain, but the background is cool.
#10. I'm not really into the ancient jungle ruins deal.
#11. I love desolate deserts like that. Very good lighting. But, PLEASE, get some new trees.
#12. Again... the hell...? Looks like a forest, and a damn weird one at that. Still looks cool, though.
#13. Very good snowscape. Could use a few more plants, though.
All in all, those terrains were very good. Keep it up!!!