The OpenGL version looks really aggressively bump mapped. The Cycle's version doesn't appear to have any bump mapping enabled.
Edit: The depth of field in the Cycle's version also looks a bit weird, and blurs away most of the terrain's detail.
https://github.com/kosua20/GL_Template/blob/3de4e116cdd24df3...
The cycles version, on the other hand, is actually using the depth map to displace a high-res mesh -- a more general technique that should yield results as good or better than parallax mapping. I'd chalk up any perceived differences to lighting and material parameters.