I like the coastline a lot. The mountains look good too, but at the moment they are overpowering the map a bit. I'd suggest dropping the shading down from black to a mid grey. Equally toning down the line thickness you are drawing the peaks with would help. I'd recommend using a line thickness the same or smaller than the thickness you are using for your coastlines. Remember, your mountains are an illustration, whereas the coast is a boundary. On a map the boundaries should be as prominent or more do than the illustrations (well, that's just my opinion).

The alternative would be to bump up the line thickness and darkness of your coastlines.

Another possible way to extend this map would be to have the mountains drop down into smaller hills as you go to the edge of the mountainous region. This would allow for a more gradual transition to and from the mountainous region.

It's a very promising style so far. Definitely keep posting and we'll keep chipping in with opinions!