Attached Link: http://img.thesun.co.uk/multimedia/archive/00423/mars2_682_423046a.jpg

 I think the scene you've got now allows very well to do the DOF effect with some postwork in photoshop, it'd really cut down your render times that way. Also, have you tried rendering without TA? the shadows look very dark and black so i suspect the TA doesnt really make much visual difference right now. I like the texture on the ground, thou maybe the rocks could have a little bit of a different color from the sand, like on many mars photographs.

The hills are too smooth as others said, probably you could try adding some amounts of noise and variation in the texture to simulate a more rocky and rough surface.

Also, in the terrain editor theres a terrain fractal that cretaes a kinda wave appearence.. ridged perlin or somethin similar, you could attempt to fade something like that in a little bit to get the subtly sweeping varieties of shape as seen on some martian photos (like the one at the link attached) that might break up the shapes on the near ground a little, as well as the hill on the left thats still somewhat in focus

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