I can't tell what 4 or 6 are meant to be representing, a little reworking for clarity would be good. The others have a very nice and clear silhouette which makes it easy to see which is which at a glance. The vines on 4 especially are confusing and would probably be worse to someone who's color blind. Other than that I just think this is really lovely. The woodcut print aspect is my favorite part, lends a lot of old world style. I feel I should be learning from you instead of the other way around. 
Thank you for the great feedback! It's funny you should call out those two in particular for reworking.
IV (4) - 'Tanglebind' (an overgrown jungle) was the absolute first pixel I laid down for the whole map (before the terrain, sea, anything). I began to rework it before I submitted for comment but my impatience won out. I agree it's not as good as it can be and think I will rework the background leaves (colour particularly) to ensure the vines pop more. Limited palette gives me grief sometimes!
VI - (6) - 'Ebonmist' (ruined castle) was the second "feature point" I completed (again, before all else) and I agree, could use some reworking. I found that I tried to put too much detail into my initial work/sections.
Thanks again!
