It may be too late to tweak continent shapes, but you have a bit of the "fill the rectangular page" thing going. See if you can render at least the raw shapes in other projections, and watch how they look more or less believable.

Your rivers make good sense.

If you're going to have the oceans so dark, consider flipping their labels to light instead of dark. I can't promise that'll look great, but you do have a contrast problem with dark-on-dark.