My first vote goes to Ascension. Very clever concept and beautifully executed terrain. I'd like to see some labels and icons to turn it into an actual map, though.

Vote #2 is for torq. There is very little to complain about concerning this map. The only thing that bothers me about it is the prominence of the rivers. Both their width and the dark stroke cause them to overshadow the other topographical features. This is, however, a challenge about rivers, so I suppose that's not a terrible flaw.

#3: RobA. You thoroughly nailed HandsomeRob's style. I'd like to see you bring some of your own personality to it, though.

And the fourth vote is for Overwatch. Once more, a unique concept and superb bit of artwork. Some explanation of what your symbols mean would be helpful. The flags and arrows are obvious enough, but I couldn't puzzle out what the boxes with x's in them were. I haven't seen much of your work yet here, but what I have has been rather monochromatic. That may just be a coincidence, but if, like me, you're nervous about color, there are some excellent links to online color scheme generators in the Reference Material forum. I have found them invaluable.