The rivers look ok at screen size, but at poster size the blunt ends will bug you. I don't use Photoshop, but I bet there's a way to taper them. For that matter, on several square feet of paper you may wish you had a more finely branched river network.
What size are you building this at?
The mountains that are midway between rust and crumpled tinfoil look pretty good, but the really smooth flatlands are way devoid of interest by comparison. Maybe they could stand a little bit of texture too? If the final product will have the flatlands filled with symbols and labels, that might suffice.