The Dunjinni user forums have a lot of things for making the transitions from water to land...things like cliffs (scale them down of course), sidewalk transitions, river banks, etc. That blocky feel seems to come from the composition itself rather than any texturing or objects. The island in the middle is rather rectangular with a rather straight-line creek on the left, stuff in the lower middle and lower right.

The map looks great but if you want to make some changes then try this on for size (although I wouldn't touch it): the skinny landmass on the left with the straight creek...trying varying that shape much more but not too skinny in the middle as it will start to make the island look "outlined" by the water...make it fatter in the middle and skinnier at the bottom; try removing the stuff in the lower middle of the image and lastly try to break up the rectangular shape of the central island. As I said before I think it looks great so these are only things that might help. Cheers.