I agree with Atpollard.
I guess, you could increase the depth on the bump map for your mountainous area. Maybe try inverting it, maybe it will help.

You could also try layering the mountains, maybe using different colours. Blur the various layers using the Gaussian blur to make the transition less stark and then bump these too, with higher and higher bump depth as the ground becomes more and more rocky...
This way, you can also had more layers toward the back of the mountains, where they are higher...

Also, as Atpollard said, shadows do great to convey an impression of depth.
In fact, you could probably try to put a black and white gradient from North to South. Then, use transparency to make the lowland more shaded than the highlands...


My final two thoughts: I feel the white aura surrounding the rocks in the ocean look a bit weird. Personally, I'd try making them a very light shade of blue. Maybe blurring them too... (I love Gaussian blur).
My second thought was regarding the roads on the East side. I guess the Easternmost road is heading toward a bridge to the island, and the second easternmost one goes toward a mountainous pass, but I am not sure about the third one. Will there be a village there? Personally, I think I'd use smaller roads there, because I don't think they'd be as important as the other ones...


Anyway, this is just some remarks I had but, as you may notice, I am quite the beginner too so, it's all tentative on my part...