Here are a couple of things i noticed.

First, I really like your coloring. works really well. The rocky areas look a little too random for me. usually when i look at maps, there is some suggestion of pattern (whether it be weather wear, or ancient glacial recession, etc. (Just an idea).

The lake looks a little angular (along with the island). Looks more like a man made lake than a natural one. I would suggest adding some Greeblies to the mix. Break up the straight lines a bit.

i'm sure some of the more experienced ppl will give you better suggestions,

GL
Marc