I really like the color scheme you've got going there; everything blends really well, and the pattern in the desert looks especially good. If I had to pick one thing that bugs me, I'd say it's the massive amount of ocean; having that much open space around the landmass makes the whole map look unbalanced somehow. If you were to cut off that entire western ocean and move the scale bar and title graphic over, I think it might balance out better.

Also, your rivers appear to be different colors from place to place (although that might be intentional), and they're hard to see in the Jenam Valley region.

As for mountains, you might try Pasis' mountain tutorial; that might be just the ticket for this map.

Overall, it looks very good though. Have some rep!