LegioCorvus
Prince
In Civ 5 they have made the sea darker - I really like how the sea looks - but they made the river lighter, and it looks weird.
That's what sticks out the most for me - by far.
As another poster said, Civ 5 rivers look anything but organic, and since that really sticks out.
That was less of an issue for me at first, and maybe the river from the video is a bad example, but it's so excessively straight as to be unrealistic. It really does stand out.