It looks like you're off to a strong start; before you start working on anything more involved--climatological or demographic mapping--I'd suggest a few minor tweaks to improve the legibility of the map. First off, the contrast between that bright white (it appears to be #ffffff) is difficult to look at directly, even more so when contrasted against very dark features. Lowering the contrast even a small amount can have a very significant impact: try using #f8f8f8 as your brightest tone, and #1b1b1b as your darkest tone. Second, can you provide us with a scale, so we know roughly how much space we're looking at?
Third and finally, I would ask what sort of elevations the various sizes of mountains represent, because if this map is a very small scale, then those major mountains rising from the island could possibly be more abrupt than you'd intended.
Otherwise, it's clean, the brushes are pleasant, and I look forward to seeing more.