One thing I've learned from making tons of TG renders is that you need some kind of focus point in the image. Something that makes it stand out. Right now, the terrain straight ahead from the camera is very closed and unexciting. Because of this, the whole image becomes unexciting. Camera placement is a HUGE factor in making any kind of render or photograph look good. Usually looking down at the terrain from a higher vantage point is only done when there is something very interesting you want the viewer to observe, otherwise its kind of like an artistic dead-end in most cases. One exception to this is if you can give a sense of depth by placing the camera near some high-up piece of terrain so that you have a foreground, middle area, and background. Try moving the camera closer to the planet surface, maybe by the shoreline at human perspective height, or maybe higher up on the cliffside, and see if you can get a more interesting view.
The surfaces could also use some more work, try loading up on some fake stones shaders... they really do go a long way towards realism. I would check out some of the grass models available on these forums as well and try experimenting with those.
Hope this helps, good luck!
