Better graphics! More polygons used for the ground. More polygons used as grass to cover the ground. Bump mapping, perhaps, for the ground textures? I don't know, just something that fools me into thinking it's ground, not just a few ugly textured polygons.
Everything else about Crysis looks so unbelievably good that such an apparent flaw in the picture becomes extra noticeable.
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I'd imagine that while moving around, as in running, which it appears will be the case throughout a good bit of the game, the "flaw" in the ground will be much less noticeable.