Very cool terrain. I like how it's this one giant piece of epicness. I dig the grass too, but have to agree that maybe it's too green, but only around the lower portions of the image.
That's actually a good example (for me, anyway) of the difference you can get from regular images and the HRD ones. I've always been meaning to play around with the .exr format, but up until last night I've just never really seen the benifit in it - partly because I've never had access to a program that can do anything useful with .exr's, partly because I've always had to work with GI off, and partly because I've never really seen a side-to-side comparison.