The only thing I find unrealistic about this one is the size proportionality. The tree on the right is a massive giant compared to the forests on the on ground next to and in the valleys by the giant tree. Other than that it is very realistic. =)
Well, in that case (being grass) it looks as if the tree should be a bit bigger... but anyway, that's just my humble opinion, and I think it's really great, and I might just use it for something. ^_~